Identification of five different insulin-like growth factor binding proteins (IGFBPs) from adult rat serum and molecular cloning of a novel IGFBP-5 in rat and human

Insulin-like growth factor binding protein 5b of Trachinotus ovatus and its heparin-binding motif play a critical role in host antibacterial immune responses via NF-κB pathway

Introduction

Insulin-like growth factor binding protein 5 (IGFBP5) exerts an essential biological role in many processes, including apoptosis, cellular differentiation, growth, and immune responses. However, compared to mammalians, our knowledge of IGFBP5 in teleosts remains limited.

Methods

In this study, TroIGFBP5b, an IGFBP5 homologue from golden pompano (Trachinotus ovatus) was identified. Quantitative real-time PCR (qRT-PCR) was used to check its mRNA expression level in healthy condition and after stimulation. In vivo overexpression and RNAi knockdown method were performed to evaluate the antibacterial profile. We constructed a mutant in which HBM was deleted to better understand the mechanism of its role in antibacterial immunity. Subcellular localization and nuclear translocation were verified by immunoblotting. Further, proliferation of head kidney lymphocytes (HKLs) and phagocytic activity of head kidney macrophages (HKMs) were detected through CCK-8 assay and flow cytometry. Immunofluorescence microscopy assay (IFA) and dual luciferase reporter (DLR) assay were used to evaluate the activity in nuclear factor-κB (NF-κβ) pathway.

Results

The TroIGFBP5b mRNA expression level was upregulated after bacterial stimulation. In vivo, TroIGFBP5b overexpression significantly improved the antibacterial immunity of fish. In contrast, TroIGFBP5b knockdown significantly decreased this ability. Subcellular localization results showed that TroIGFBP5b and TroIGFBP5b-δHBM were both present in the cytoplasm of GPS cells. After stimulation, TroIGFBP5b-δHBM lost the ability to transfer from the cytoplasm to the nucleus. In addition, rTroIGFBP5b promoted the proliferation of HKLs and phagocytosis of HKMs, whereas rTroIGFBP5b-δHBM, suppressed these facilitation effects. Moreover, the in vivo antibacterial ability of TroIGFBP5b was suppressed and the effects of promoting expression of proinflammatory cytokines in immune tissues were nearly lost after HBM deletion. Furthermore, TroIGFBP5b induced NF-κβ promoter activity and promoted nuclear translocation of p65, while these effects were inhibited when the HBM was deleted.

Discussion

Taken together, our results suggest that TroIGFBP5b plays an important role in golden pompano antibacterial immunity and activation of the NF-κβ signalling pathway, providing the first evidence that the HBM of TroIGFBP5b plays a critical role in these processes in teleosts.

IGF-Binding Proteins and Their Proteolysis as a Mechanism of Regulated IGF Release in the Nervous Tissue

Insulin-like growth factors 1 and 2 (IGF-1 and IGF-2) play a key role in the maintenance of the nervous tissue viability. IGF-1 and IGF-2 exhibit the neuroprotective effects by stimulating migration and proliferation of nervous cells, activating cellular metabolism, inducing regeneration of damaged cells, and regulating various stages of prenatal and postnatal development of the nervous system. The availability of IGFs for the cells is controlled via their interaction with the IGF-binding proteins (IGFBPs) that inhibit their activity. On the contrary, the cleavage of IGFBPs by specific proteases leads to the IGF release and activation of its cellular effects. The viability of neurons in the nervous tissue is controlled by a complex system of trophic factors secreted by auxiliary glial cells. The main source of IGF for the neurons are astrocytes. IGFs can accumulate as an extracellular free ligand near the neuronal membranes as a result of proteolytic degradation of IGFBPs by proteases secreted by astrocytes. This mechanism promotes interaction of IGFs with their genuine receptors and triggers intracellular signaling cascades. Therefore, the release of IGF by proteolytic cleavage of IGFBPs is an important mechanism of neuronal protection. This review summarizes the published data on the role of IGFs and IGFBPs as the key players in the neuroprotective regulation with a special focus on the specific proteolysis of IGFBPs as a mechanism for the regulation of IGF bioavailability and viability of neurons.

Molecular regulation of phenolic compounds on IGF-1 signaling cascade in breast cancer

Breast cancer is a highly aggressive and heterogeneous disease with complex features that remains a major health problem and undermines the span and quality of life of women worldwide. Primary literature has shown the role of phenolic compounds in controlling the onset of breast cancer. The mechanism of action of phenolic compounds can be explained by their interaction with signal transduction pathways that regulate cell proliferation and induction of apoptosis. One of the targets of phenolic compounds is the insulin like growth factor 1 (IGF-1) signaling cascade, which plays a significant role in the growth and development of mammary tissues by leading proliferative and anti-apoptotic events. Increasing research evidence points to the function of the IGF-1 cascade system in the commencement, progression, and metastasis of breast tissue malignancy. In this review, we mainly discuss the function of the IGF-1 system, and the role of phenolic compounds in regulating the IGF-1 signaling cascade and curbing breast malignancies.

Biological effects and regulation of IGFBP5 in breast cancer

The insulin-like growth factor receptor (IGF1R) pathway plays an important role in cancer progression. In breast cancer, the IGF1R pathway is linked to estrogen-dependent signaling. Regulation of IGF1R activity is complex and involves the actions of its ligands IGF1 and IGF2 and those of IGF-binding proteins (IGFBPs). Six IGFBPs are known that share the ability to form complexes with the IGFs, by which they control the bioavailability of these ligands. Besides, each of the IGFBPs have specific features. In this review, the focus lies on the biological effects and regulation of IGFBP5 in breast cancer. In breast cancer, estrogen is a critical regulator of IGFBP5 transcription. It exerts its effect through an intergenic enhancer loop that is part of the chromosomal breast cancer susceptibility region 2q35. The biological effects of IGFBP5 depend upon the cellular context. By inhibiting or promoting IGF1R signaling, IGFBP5 can either act as a tumor suppressor or promoter. Additionally, IGFBP5 possesses IGF-independent activities, which contribute to the complexity by which IGFBP5 interferes with cancer cell behavior.

Insulin-Like Growth Factor Binding Protein-5 in Physiology and Disease

Insulin-like growth factor (IGF) signaling is regulated by a conserved family of IGF binding proteins (IGFBPs) in vertebrates. Among the six distinct types of IGFBPs, IGFBP-5 is the most highly conserved across species and has the broadest range of biological activities. IGFBP-5 is expressed in diverse cell types, and its expression level is regulated by a variety of signaling pathways in different contexts. IGFBP-5 can exert a range of biological actions including prolonging the half-life of IGFs in the circulation, inhibition of IGF signaling by competing with the IGF-1 receptor for ligand binding, concentrating IGFs in certain cells and tissues, and potentiation of IGF signaling by delivery of IGFs to the IGF-1 receptor. IGFBP-5 also has IGF-independent activities and is even detected in the nucleus. Its broad biological activities make IGFBP-5 an excellent representative for understanding IGFBP functions. Despite its evolutionary conservation and numerous biological activities, knockout of IGFBP-5 in mice produced only a negligible phenotype. Recent research has begun to explain this paradox by demonstrating cell type-specific and physiological/pathological context-dependent roles for IGFBP-5. In this review, we survey and discuss what is currently known about IGFBP-5 in normal physiology and human disease. Based on recent in vivo genetic evidence, we suggest that IGFBP-5 is a multifunctional protein with the ability to act as a molecular switch to conditionally regulate IGF signaling.

Sex-specific correlation of IGFBP-2 and IGFBP-3 with vitamin D status in adults with obesity: a cross-sectional serum proteomics study

Objective

Subjects with low vitamin D levels are at risk of cardiometabolic disease. The aim of this study was to identify novel serological markers linking vitamin D status with cardiometabolic profile in non-diabetic adults with obesity.

Methods

For the discovery phase, we used quantitative serum proteomics in sex-matched, age-matched and BMI-matched subjects with obesity [BMI: 25–35 kg/m²] and low [25(OH)D < 50 nmol/L] vs. high vitamin D status [25(OH)D > 50 nmol/L] (n = 16). For the validation phase, we performed ELISA in a larger cohort with similar characteristics (n = 179).

Results

We identified 423 and 549 differentially expressed proteins in the high vs. low vitamin D groups of the male and female cohorts, respectively. The small molecule biochemistry protein networks and the glycolysis|gluconeogenesis pathway were significantly enriched in the DEPs of both sexes. As surrogate markers to these processes, the insulin-like growth factor binding protein -2  (IGFBP-2) was upregulated in males, whereas   IGFBP-3 was upregulated in females from the high Vitamin D status. This sex-specific trend  was confirmed using Luminex ELISA to an independent but clinically analogous cohort of males (n = 84, p = 0.002) and females (n = 95, p = 0.03).

Conclusions

The high Vitamin D status correlated with the serological upregulation of IGFBP-2 in males and IGFBP-3 in females with obesity and may constitute surrogate markers of risk reduction of cardiometabolic disease.

Trajectories of IGF-I Predict Mortality in Older Adults: The Cardiovascular Health Study

Background

Disruption of insulin-like growth factor-I (IGF-I) increases health and life span in animal models, though this is unconfirmed in humans. If IGF-I stability indicates homeostasis, the absolute level of IGF-I may be less clinically relevant than maintaining an IGF-I setpoint.

Methods

Participants were 945 U.S. community-dwelling individuals aged ≥65 years enrolled in the Cardiovascular Health Study with IGF-I levels at 3-6 timepoints. We examined the association of baseline IGF-I level, trajectory slope, and variability around the trajectory with mortality.

Results

There were 633 deaths over median 11.3 years of follow-up. Lower IGF-I levels, declining or increasing slope, and increasing variability were each individually associated with higher mortality (all p < .001). In an adjusted model including all three trajectory parameters, baseline IGF-I levels <70 ng/mL (hazard ratio [HR] 1.58, 95% CI 1.28-1.96 relative to IGF-I levels of 170 ng/mL), steep declines and steep increases in trajectory slope (HR 2.22, 1.30-3.80 for a 15% decline; HR 1.40, 1.07-1.84 for a 10% decline; HR 1.80, 1.12-2.89 for a 15% increase; HR 1.31, 1.00-1.72 for a 10% increase, each vs no change), and variability ≥10% (HR 1.59, 1.09-2.32 for ≥ 30%; HR 1.36, 1.06-1.75 for 20%; and HR 1.17, 1.03-1.32 for 10% variability, each vs 0%) in IGF-I levels were independently associated with mortality.

Conclusions

In contrast to data from animal models, low IGF-I levels are associated with higher mortality in older humans. Irrespective of the actual IGF-I level, older individuals with stability of IGF-I levels have lower mortality than those whose IGF-I levels fluctuate over time.

The Association Between IGF-I and IGFBP-3 and Incident Diabetes in an Older Population of Men and Women in the Cardiovascular Health Study

CONTEXT

Insulin-like growth factor-I (IGF-I) has structural and functional similarities to insulin and may play a role in glucose homeostasis, along with insulin-like growth factor binding protein-3 (IGFBP-3), which binds the majority of circulating IGF-I.

OBJECTIVE

To assess whether IGF-I and IGFBP-3 are associated with a higher risk of incident diabetes in older adults.

DESIGN

Participants in the Cardiovascular Health Study (n = 3133), a cohort of adults aged ≥65 years, were observed for 16 years (n = 3133) for the development of incident diabetes. Statistical models were fit separately for men and women because of interactions with sex (P interaction: IGF-I, 0.02; IGFBP-3, 0.009) and were adjusted for relevant covariates.

SETTING

General community.

PARTICIPANTS

Older adults who were nondiabetic at baseline and who did not develop diabetes within the first year of follow-up.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Incident diabetes as measured by fasting plasma glucose (FPG) ≥126 mg/dL, non-FPG ≥200 mg/dL, use of pharmacological treatment of diabetes, or existence of two or more inpatient or three or more outpatient or (at least one inpatient and at least one outpatient) Centers for Medicare & Medicaid Services claims with the diagnostic International Classification of Diseases, Ninth Revision, Clinical Modification code of 250.xx.

RESULTS

In women, higher IGFBP-3 (hazard ratio tertile 3 vs tertile 1 = 2.30; 95% confidence interval, 1.55 to 3.40; P trend < 0.0001) was significantly associated with incident diabetes. Total IGF-I was not significantly associated with incident diabetes. In men, neither IGF-I nor IGFBP-3 was significantly associated with incident diabetes.

CONCLUSIONS

We confirmed a previously reported association between circulating IGFBP-3 and diabetes risk in the older adult population, establishing that this association is present among women but could not be shown to be associated in men.

IGFBP-4 expression is adversely associated with lung cancer prognosis

Insulin-like growth factor binding protein-4 (IGFBP-4) was reported to be associated with prognosis in several types of cancer; however, to the best of our knowledge, whether it is correlated with lung cancer has yet to be reported. In the present study, 102 pairs of lung cancer tissues and surrounding non-cancerous tissues (SNCTs) were collected. The IGFBP-4 levels in tissues were detected with immunohistochemistry. The relevance of IGFBP-4 to the survival of patients was assessed. The IGFBP-4 gene was knocked down, and its function in the proliferation of lung cancer cells was measured. The percentage of lung cancer tissues with higher IGFBP-4 expression than SNCTs (51.9%) was increased compared with the percentage with similar (11.76%) or lower (36.27%) IGFBP-4 expression. Patients with higher IGFBP-1 expression exhibited a shorter median survival time. IGFBP-1 was associated with metastasis, lung cancer stages and malignancy, but not with age, sex or tumor size. Lung cancer cells with stably knocked down IGFBP-4 showed an inhibitory proliferation rate. The present study identified that IGFBP-4 was adversely associated with the prognosis of lung cancer patients. IGFBP-4 knockdown prohibited lung cancer cell growth. The present study provides a potential marker for lung cancer diagnosis and a possible target for lung cancer therapy.

Insulinlike Growth Factor Binding Protein-1 and Ghrelin Predict Health Outcomes Among Older Adults: Cardiovascular Health Study Cohort

CONTEXT

Multiple diseases may explain the association of the growth hormone/insulinlike growth factor-I (GH/IGF-I) axis with longevity.

OBJECTIVE

To relate circulating GH/IGF-I system protein levels with major health events.

DESIGN AND SETTING

This is a cohort study set in 4 US communities.

PARTICIPANTS

Adults (N = 2268) 65 years and older free of diabetes and cardiovascular disease.

MEASUREMENTS

We assessed insulinlike growth factor binding protein-1 (IGFBP-1) and ghrelin in fasting and 2-hour oral glucose tolerance test (OGTT) blood samples, as well as fasting IGF-I and IGFBP-3. Hazard ratios for mortality and a composite outcome for first incident myocardial infarction, stroke, heart failure, hip fracture, or death were adjusted for sociodemographic, behavioral, and physiological covariates.

RESULTS

During 13,930 person-years of follow-up, 48.1% of individuals sustained one or more components of the composite outcome and 31.8% died. Versus the lowest quartiles, the highest quartiles of fasting and 2-hour ghrelin were associated with 27% higher (95% confidence interval [CI]: 6%, 53%) and 39% higher (95% CI: 14%, 71%) risks of the composite outcome, respectively. The highest quartile of 2-hour IGFBP-1 was associated with 35% higher (95% CI: 1%, 52%) risk of the composite end point. Similarly, higher mortality was significantly associated with higher fasting and 2-hour ghrelin levels and with 2-hour IGFBP-1 level. When examined together, 2-hour post-OGTT levels of IGFBP-1 and ghrelin tended to predict outcomes better than fasting levels.

CONCLUSIONS

Circulating IGFBP-1 and ghrelin measured during an OGTT predicted major health events and death in older adults, which may explain the influence of the GH/IGF-I axis on lifespan and health.

Two grass carp (Ctenopharyngodon idella) insulin-like growth factor-binding protein 5 genes exhibit different yet conserved functions in development and growth

Insulin-like growth factor binding-protein 5 (igfbp5), the most conserved member of the IGFBP family in vertebrates, plays a critical role in controlling cell survival, growth, differentiation, and apoptosis. Here, we characterized the expression patterns of igfbp5a and igfbp5b in grass carp (Ctenopharyngodon idella), which are retained in many fish species, likely from the teleost-specific whole-genome duplication. Both igfbp5a and igfbp5b encode 268- and 263-aa peptides, respectively, which share a sequence identity of 71%. Their mRNAs are not detected in zygotes. At 14hpf, grass carp igfbp5b mRNA was detected in the somites, while igfbp5a mRNA has some possible signal around the eye and head region. At 24hpf, both igfbp5a and igfbp5b mRNA appear to be limited to the presomitic mesoderm. At 36hpf, igfbp5a mRNA was only detected in the midbrain, while igfbp5b mRNA was detected in both the midbrain and notochord. Overall, both mRNAs were expressed in most adult tissues. igfbp5a and igfbp5b were significantly upregulated in the muscle and liver after injection of 10μg per kilogram body weight of zebrafish growth hormone (zGH), while their hepatic expression was downregulated by 50μg zGH. During fasting, both igfbp5a and igfbp5b mRNAs were significantly downregulated in the muscle but upregulated in the liver. Collectively, the results suggest that the two igfbp5 genes play important but different roles in the regulation of growth and development in grass carp.

Agreement between circulating IGF-I, IGFBP-1 and IGFBP-3 levels measured by current assays versus unavailable assays previously used in epidemiological studies

OBJECTIVE

Levels of insulin-like growth factor (IGF) proteins are associated with the risk of cancer and mortality. IGF assays produced by Diagnostic Systems Laboratories (DSL) were widely used in epidemiological studies, were not calibrated against recommended standards and are no longer commercially available.

DESIGN

In a split sample study among 1471 adults participating in the Cardiovascular Health Study, we compared values obtained using DSL assays with alternative assays for serum IGF-I (Immunodiagnostic Systems, IDS), IGFBP-1 (American Laboratory Products Company, ALPCO) and IGFBP-3 (IDS).

RESULTS

Results were compared using kernel density estimation plots, quartile analysis with weighted kappa statistics and linear regression models to assess the concordance of data from the different assays. Participants had a mean age of 77years. Results between alternative assays were strongly correlated (IGF-I, r=0.93 for DSL versus IDS; log-IGFBP-1, r=0.90 for DSL versus ALPCO; IGFBP-3, r=0.92 for DSL versus IDS). Cross tabulations showed that participants were usually in the same quartile categories regardless of the assay used (overall agreement, 74% for IGF-I, 64% for IGFBP-1, 71% for IGFBP-3). Weighted kappa also showed substantial agreement between assays (kw, 0.78 for IGF-I, 0.69 for IGFBP-1, 0.76 for IGFBP-3). Regressions of levels obtained with DSL assays (denoted X) to alternative assays were, IGF-I: 0.52X+15.2ng/ml, log-IGFBP-1: 1.01X-1.73ng/ml IGFBP-3: 0.87X+791.1ng/ml. Serum values of IGF-I, IGFBP-1 and IGFBP-3 measured using alternative assays are moderately correlated.

CONCLUSIONS

Care is needed in the interpretation of data sets involving IGF analytes if assay methodologies are not uniform.

Identification and characterization of cancer mutations in Japanese lung adenocarcinoma without sequencing of normal tissue counterparts

We analyzed whole-exome sequencing data from 97 Japanese lung adenocarcinoma patients and identified several putative cancer-related genes and pathways. Particularly, we observed that cancer-related mutation patterns were significantly different between different ethnic groups. As previously reported, mutations in the EGFR gene were characteristic to Japanese, while those in the KRAS gene were more frequent in Caucasians. Furthermore, during the course of this analysis, we found that cancer-specific somatic mutations can be detected without sequencing normal tissue counterparts. 64% of the germline variants could be excluded using a total of 217 external Japanese exome datasets. We also show that a similar approach may be used for other three ethnic groups, although the discriminative power depends on the ethnic group. We demonstrate that the ATM gene and the PAPPA2 gene could be identified as cancer prognosis related genes. By bypassing the sequencing of normal tissue counterparts, this approach provides a useful means of not only reducing the time and cost of sequencing but also analyzing archive samples, for which normal tissue counterparts are not available.

Effect of shock wave treatment on platelet-rich plasma added to osteoblast cultures

The aim of this study was to verify the effects on osteoblast cultures of adding a platelet-rich plasma (PRP) concentrate pretreated with 500 shock wave (SW) at an energy flow density of 0.17 mJ/mm(2), emitted by an electromagnetic generator Minilith SL1 (STORZ, Germany), reproducing the conditions of our previous study in which we apply SW directly on osteoblasts. Real-time PCR showed that in osteoblast cultures with added PRP pretreated with SW, there was an increased expression at 48 h of insulin-like growth factor binding protein 3 (IGFBP-3) and runt-related transcription factor 2 (RUNX2) and at 72 h, of collagen type I, osteocalcin, insulin-like growth factor 1 (IGF-1) as well as IGFBP-3. Western blotting confirmed the increased protein synthesis of IGFBP-3. This experience suggests that extracorporeal shock wave treatment (ESWT) should stimulate osteogenesis also by indirect platelets-mediated network. It therefore seems possible that combining the two methods, ESWT and bioengineering procedures to infiltrate PRP and growth factors, could be a successful approach.

Insulin-like growth factors and their binding proteins in domestic animals

Insulin-like growth factors (IGFs) and their binding proteins play an essential role in regulating animal growth and metabolism. The initial portion of the current review focuses on the physiological effects of the IGFs and delineates their role as regulators of animal growth and metabolism. The role of IGFs as mediators of growth hormone effects, as insulin-like metabolic regulators and as foetal growth regulators is discussed. The remainder of the review is devoted to the IGF binding proteins, their modulation of IGF action and their role in foetal and postnatal regulation of growth.

The relationship between maternal insulin-like growth factors 1 and 2 (IGF-1, IGF-2) and IGFBP-3 to gestational age and preterm delivery

AIMS

To investigate the relationship between levels of insulin-like growth factors 1 and 2 (IGF-1, IGF-2), and insulin-like growth factor binding protein 3 (IGFBP-3) in antenatal maternal serum and gestational age at delivery.

METHODS

Prospective cohort study of 1650 low-risk Caucasian women in a London University teaching hospital. Maternal IGF-1, IGF-2 and IGFBP-3 were measured in maternal blood at booking and analyzed with respect to gestational age at delivery.

RESULTS

There was no significant association between maternal IGF-1 or IGF-2 and preterm birth (PTB). A significant reduction in mean IGFBP-3 levels was noted with delivery <32 completed weeks (P=0.02).

CONCLUSION

Maternal mean IGFBP-3 levels are significantly reduced in cases complicated by delivery <32 completed weeks.

Association of porcine IGF binding protein-5 gene with meat quality

IGFBP-5 is a member of the IGF families. Using PCR-SSCP, genotypic and allelic frequencies were analyzed in 18 pig breeds (n = 600). The association between haplotypes and production performance was analyzed in a Jinhua x Pietrain population family (n = 212, total 24 traits). Two SNPs (T199C and G485A) within the gene were analyzed. The breeds had different genotypic and allelic frequencies. Typically, the Chinese native pig breeds carried a higher allele C and G frequency (over 50%) than those of the European pigs, and only Guangdong Large White and wild boar were at Hardy-Weinberg equilibrium. The pigs carrying the CG haplotype had higher hue, loin, and thigh pH1 values than pigs with the TA haplotype, and pigs with the TA haplotype had the lowest loin pH2 value and highest color-a value among the haplotypes. It is proposed that the IGFBP-5 gene is associated with the variation in meat quality, especially in pH value together with other QTLs on chromosome 15.

Transgenic overexpression of pregnancy-associated plasma protein-A increases the somatic growth and skeletal muscle mass in mice

Although IGFs are indispensable to skeletal muscle development, little information is available regarding the mechanisms regulating the local action of IGFs in skeletal muscle tissues. Here we tested the hypothesis that pregnancy-associated plasma protein-A (PAPP-A), a member of the metalloproteinase superfamily, promotes skeletal muscle formation in vivo through degrading IGF binding proteins (IGFBPs), which increases the bioavailability of IGFs. Expression of PAPP-A is significantly increased in muscle five days after muscle injury in mice. Targeted overexpression of PAPP-A using a muscle-specific promoter significantly increased the prenatal/postnatal growth, skeletal muscle weight, and muscle fiber area in mice. These anabolic effects were reproduced using F2/F3 progeny. Free IGF-I concentration was severalfold higher in the conditioned medium (CM) of ex vivo cultured muscle from the transgenic mice, compared with the wild-type littermate muscle. Accordingly, the proliferation of C2C12 myoblasts was significantly increased in the presence of CM from cultured skeletal muscle of the transgenic mice, compared with the controls. This observed increase in myoblast proliferation was abolished on addition of noncleavable IGFBP-4 peptide, which reduced free IGF-I concentration back to the basal level of the wild-type CM. Furthermore, proliferation and differentiation of C2C12 myoblasts was increased by transient overexpression of proteolytically active PAPP-A but not by inactive mutant PAPP-A (E483/A). Collectively, we identified PAPP-A as a novel regulator of prenatal/postnatal growth and skeletal muscle formation in vivo. Moreover, our studies provide the first experimental evidence that IGFBP degradation is a key determinant in modulating the local action of IGFs in muscle.

Insulin-like growth factor binding proteins in follicular fluid from morphologically distinct healthy and atretic bovine antral follicles

In bovine follicles 2-5 mm in diameter, two morphologically distinct types of healthy follicles and two types of atretic follicles have been described recently. Healthy follicles either have columnar basal granulosa cells with follicular basal lamina composed of many layers or 'loops' or they have rounded basal cells with a conventional single-layered, aligned follicular basal lamina. In atretic follicles, cell death either commences at the basal layer and progresses to the antrum (basal atresia) with macrophage penetration of the membrana granulosa or death progresses from the antrum in a basal direction (antral atresia). Little is known about how these different phenotypes develop. To determine whether insulin-like growth factor binding protein (IGFBP) levels in follicular fluid differ between these different types of follicles, we measured IGFBP levels in fluids from these follicles. A total of 61 follicles were assessed by light microscopy and characterized by morphological analysis as either healthy, with columnar or rounded basal granulosa cells, or as undergoing antral or basal atresia. The IGFBP concentration in the follicular fluid of individual follicles from the four groups (n = 12-20 per group) was identified by Western ligand blots using (125)I-insulin-like growth factor (IGF)-II as a probe. Insulin-like growth factor binding proteins 2, 3 (44 and 40 kDa), 4 (glycosylated and non-glycosylated) and 5 were observed. The levels (per volume of fluid) of IGFBPs 2, 4 and 5 were greater in atretic follicles than in healthy follicles. However, there were no statistical differences in levels of each IGFBP between either the two types of healthy follicle or between the two types of atretic follicles. Thus, IGFBP levels are not related to the different types of healthy or atretic follicles.

The Basic Science of Wound Healing

Understanding wound healing today involves much more than simply stating that there are three phases: "inflammation, proliferation, and maturation." Wound healing is a complex series of reactions and interactions among cells and "mediators." Each year, new mediators are discovered and our understanding of inflammatory mediators and cellular interactions grows. This article will attempt to provide a concise report of the current literature on wound healing by first reviewing the phases of wound healing followed by "the players" of wound healing: inflammatory mediators (cytokines, growth factors, proteases, eicosanoids, kinins, and more), nitric oxide, and the cellular elements. The discussion will end with a pictorial essay summarizing the wound-healing process.

Insulin-like growth factor-binding protein-5 (IGFBP-5): a critical member of the IGF axis

The six members of the insulin-like growth factor-binding protein family (IGFBP-1-6) are important components of the IGF (insulin-like growth factor) axis. In this capacity, they serve to regulate the activity of both IGF-I and -II polypeptide growth factors. The IGFBPs are able to enhance or inhibit the activity of IGFs in a cell- and tissue-specific manner. One of these proteins, IGFBP-5, also has an important role in controlling cell survival, differentiation and apoptosis. In this review, we report on the structural and functional features of the protein which are important for these effects. We also examine the regulation of IGFBP-5 expression and comment on its potential role in tumour biology, with special reference to work with breast cancer cells.

The Expression of Insulin-like Growth Factor and Insulin-like Growth Factor Binding Protein mRNAs in Mouse Placenta

Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) are paracrine regulators of tissue growth and development, and are expressed at the sites of biological action. To study the role of the IGFs and IGFBPs in mouse placental development, we determined the temporal and spatial expression patterns of the mRNAs at embryonic days 10.5 to 18.5 by in situ hybridization. IGF-II mRNA was expressed strongly in mesoderm and fetal blood vessels of early placenta and in labyrinthine trophoblast of later placenta. In the junctional zone, IGF-II mRNA was expressed first in spongiotrophoblasts, later strongly in glycogen cells and variably in giant cells. IGFBP-2 mRNA was expressed weakly in spongiotrophoblasts and glycogen cells. IGFBP-2, -5 and -6 mRNAs were detected in the stroma of the metrial gland. Myometrium expressed IGFBP-2 mRNA strongly, IGFBP-6 mRNA moderately and IGFBP-5 mRNA weakly. The endothelium of maternal blood vessels in decidua expressed IGFBP-3 and -5 mRNAs, and some deeper vessels expressed IGFBP-4 mRNA. In the yolk sac, IGF-II mRNA was expressed in endoderm and mesoderm, whereas IGFBP-1, -2 and -4 mRNAs were expressed only in endoderm, and IGFBP-4 mRNA in mesoderm. Strong expression of IGF-II mRNA in glycogen cells suggests a role in the autocrine/paracrine regulation of invasion. Similar to rat and guinea pig, but in contrast to man and primates, IGFBP mRNAs, except IGFBP-4, were not expressed in mouse decidua. However, IGFBP-3, -4 and -5 mRNAs were expressed in endothelium of maternal blood vessels, and IGFBP-2 and -6 mRNAs in myometrium, where IGFBPs may play a critical role in regulating trophoblast invasion. These findings suggest possible biological roles of the peptides at the feto-maternal interface.

The insulin-like growth factor-I gene and osteoporosis: a critical appraisal

Osteoporosis, a disorder of skeletal fragility, is common in the elderly, and its prevalence is increasing as more individuals with low bone mineral density (BMD), the strongest predictor of fracture risk, are detected. Previous basic and clinical studies imply there is a significant role for insulin-like growth factor-I (IGF-I) in determining BMD. Recently, polymorphisms upstream of the P1 promoter region of the human IGF-I gene have been found to be associated with serum levels of IGF-I, BMD and fracture risk in various ethnic groups. Multiple quantitative trait loci (QTLs) have been identified that underlie serum IGF-I in a mouse intercross between two inbred strains. The most promising QTL on mouse chromosome 6 has provided clues for unraveling the molecular mechanisms that regulate osteoblast differentiation. Genomic engineering resulting in IGF-I deficient mice, and mice with targeted over-expression of IGF-I reinforce the essential role of IGF-I in bone development at both the embryonic and postnatal stages. Thus, it is apparent that significant new insights into the role of the IGF-I gene in bone remodeling occur through several distinct mechanisms: (1) the skeletal IGF regulatory system; (2) the systemic growth hormone/IGF-I axis; (3) parathyroid hormone signaling; (4) sex steroids; and (5) the OPG/RANKL/RANK cytokine system. Molecular dissection of the IGF regulatory system and its signaling pathway in bone may reveal novel therapeutic targets for the treatment of osteoporosis.

Enhanced expression of insulin-like growth factor-binding proteins in human osteoarthritic cartilage detected by immunohistochemistry and in situ hybridization

OBJECTIVE

To determine the roles of insulin-like growth factor (IGF) and IGF-binding protein (IGFBP) in the pathogenesis of osteoarthritis (OA).

DESIGN

Cartilage tissues were obtained from the femoral heads of patients with OA, and those from patients with femoral neck fractures were used as a control. The expression of IGFBP-3, -4, and -5 was examined using immunohistochemistry and in situ hybridization, and IGF-I and IGF-I receptors were also immunohistochemically detected. The percentages of positive chondrocytes were determined by counting the total number of chondrocytes over the area of the surface, middle, and deep zones of the cartilage.

RESULTS

There was a marked increase in the percentage of positive chondrocytes in all IGFBPs on protein and messenger RNA levels for OA compared to that of the control cartilage. Furthermore, enhanced expression of IGFBPs and the IGF-I/IGF-I receptor was positively correlated with the histologic score for cartilage lesions.

CONCLUSION

Up-regulation of IGFBPs as well as IGF-I and its receptor was observed for OA cartilage tissue, suggesting the involvement of IGFBPs in the pathogenesis of OA.

Overexpression of IGF-binding protein 5 alters mineral and matrix properties in mouse femora: an infrared imaging study

The anabolic effects of insulin-like growth factors (IGFs) are modulated by a family of IGF-binding proteins (IGFBPs). Among the six known IGFBPs, IGFBP-5 is considered to play a role in bone formation. To investigate the effects of IGFBP-5 on bone mineral and matrix properties, femurs from transgenic mice overexpressing IGFBP-5 under the control of the osteocalcin promoter were evaluated by Fourier Transform Infrared Imaging (FTIRI). Analyses were done at the time of maximal osteocalcin expression (5 weeks). The spectroscopic parameters monitored were mineral-to-matrix ratio (indicative of the relative amount of mineral present), mineral crystallinity (index of the mineral crystal size and perfection) and collagen maturity (reflecting the ratio of non-reducible and reducible collagen cross-links). Multiple fields were selected for each femur, ranging from epiphysis to diaphysis. Previously, we showed that these transgenic mice display decreased osteoblastic function and osteopenia. In the present work, FTIRI showed that transgenic mice as compared to wild types have a different pattern of bone mineralization and matrix maturation. Specifically, cortical bone, primary spongiosa, and secondary ossification centers had lower values for mineral-to-matrix ratio and collagen maturity. Differences were not statistically significant in all cases although the trends were consistent. The mineral crystallinity did not vary significantly between the two groups, implying that the crystal maturation of mineral was not affected by IGFBP-5 overexpression. This study demonstrates that femurs from transgenic mice over expressing IGFBP-5 under the control of the osteocalcin promoter have modest alterations in mineral and matrix distribution, consistent with a role of IGF in osteoblast maturation.

Expression and characterization of a serine protease that preferentially cleaves insulin-like growth factor binding protein-5

Insulin-like growth factor binding proteins (IGFBPs) play important roles in regulating the functions of insulin-like growth factors (IGFs). Because IGFBPs have very high affinity for IGF-I and IGF-II, they can regulate the amount of each growth factor that is able to bind to cell surface receptors, therefore, factors that alter IGFBP affinity have the capacity to regulate IGF actions. Protease activities that are present in cell culture systems and physiologic fluids have been shown to degrade IGFBP-5. Previously, a region of sequence in a serine protease was identified that was homologous with the N-terminal 90 amino acids of members of the IGFBP family and with members of the CCN family of proteins. In a prior study, the protease was expressed in human kidney cultured cells and the cell culture supernatants were shown to cleave IGFBP-5, however, it is unknown whether the purified protease would cleave IGFBP-5 and whether it would also cleave other specific forms of IGFBPs. In this study, we expressed this protease in an insect cell expression system, purified it to homogeneity and tested its capacity to cleave IGFBP-5. The expressed protease preferentially cleaved IGFBP-5, and it had minimal activity toward other forms of IGFBPs. The proteolytic activity of this IGFBPase is inhibited by serine protease inhibitors including PMSF and 3,4-dichloroisocoumarin, as well as by divalent metal ions such as, Zn and Cu. Mutation of the active site serine resulted in a major reduction in IGFBP-5 cleavage. The protease binds to heparin and its ability to degrade IGFBP-5 is blocked in the presence of heparin. Inhibition of the activity of the protease following its secretion by B104 cells resulted in inhibition of IGFBP-5 proteolysis and IGF-I stimulation of protein synthesis. Northern blotting revealed that the transcript was expressed in multiple human tissues, including placenta, uterus, prostate, testis, spinal cord, brain, liver, small intestine, thyroid, and spleen. The highest expression was in uterus and placenta, suggesting a possible role of sex steroids in regulating its expression. Understanding the mechanism of how cleavage of IGFBP-5 by this protease alters its activity will help to further our understanding of the biologic actions of the IGFs.

Transgenic mice expressing selected insulin-like growth factor-binding protein-5 fragments do not exhibit enhanced bone formation

Skeletal cells synthesize insulin like growth factors (IGF) and six IGF binding proteins (IGFBP). IGFBP-5 and fragments were reported to stimulate bone cell growth and parameters of osteoblastic function. We investigated the effects of IGFBP-5 1-162 and 1-193 on bone remodeling in transgenic mice overexpressing these fragments under the control of the osteocalcin promoter. Transgenic mice had normal appearance, weight, and bone mineral density. Static and dynamic histomorphometry revealed that transgenic mice overexpressing IGFBP-5 1-162 or 1-193 had normal trabecular bone volume, osteoblast and osteoclast number, and normal bone formation rate. MC3T3 cells transduced with retroviral vectors overexpressing IGFBP-5 1-235, 1-193, and 1-162 fragments displayed normal cell growth and maturation, and failed to enhance the expression of alkaline phosphatase, osteocalcin, and type I collagen mRNA when compared to cells transduced with vector alone. In conclusion, transgenic mice expressing IGFBP-5 1-162 and 1-193 in the bone microenvironment do not exhibit an obvious skeletal phenotype.

Pregnancy-associated plasma protein-a production in rat granulosa cells: stimulation by follicle-stimulating hormone and inhibition by the oocyte-derived bone morphogenetic protein-15

Pregnancy-associated plasma protein-A (PAPP-A) is the major IGF binding protein-4 (IGFBP-4) protease in follicular fluid, consistent with its proposed role in folliculogenesis. Despite growing interest, almost nothing is known about how PAPP-A expression is regulated in any tissue. Here we show that FSH and oocytes regulate PAPP-A expression in granulosa cells (GCs). By in situ hybridization, ovary PAPP-A mRNA was markedly increased by pregnant mare serum gonadotropin treatment, and the message was localized to the membrana GCs but not cumulus GCs (CGCs) of dominant follicles. To explore the mechanism, we used primary cultures of rat GCs. Control (untreated) cells produced little or no PAPP-A spontaneously. Conversely, FSH markedly stimulated PAPP-A mRNA and protein in a dose- and time-dependent fashion. Interestingly, PAPP-A expression in isolated CGCs was also strongly induced by FSH, and the induction was inhibited by added oocytes. To investigate the nature of the inhibition, we tested the effect of oocyte-derived bone morphogenetic protein-15 (BMP-15). BMP-15 alone had no effect on basal levels of PAPP-A expression by cultures of membrana GCs or CGCs. However, BMP-15 markedly inhibited the FSH stimulation of PAPP-A production in a dose-dependent manner. The cleavage of IGFBP-4 by conditioned media from FSH-treated GCs was completely inhibited by anti-PAPP-A antibody, indicating the IGFBP-4 protease secreted by GCs is PAPP-A. These results demonstrate stimulatory and inhibitory roles for FSH and BMP-15, respectively, in regulating PAPP-A production by GCs. We propose that FSH and oocyte-derived BMP-15 form a controlling network that ensures the spatiotemporal pattern of GC PAPP-A expression in the dominant follicle.

Paradoxical actions of endogenous and exogenous insulin-like growth factor-binding protein-5 revealed by RNA interference analysis

Insulin-like growth factor-binding protein-5 (IGFBP-5) is abundantly expressed in bone cells. To determine the physiological role(s) of endogenous IGFBP-5 in regulating bone cell growth, differentiation, and survival, we used short double-stranded RNA (siRNA) to trigger RNA interference of IGFBP-5 in human osteosarcoma cells. The IGFBP-5 siRNA, targeting against a sequence unique to the IGFBP-5 middle domain, efficiently reduced IGFBP-5 mRNA and protein levels. The IGFBP-5 siRNA did not change the levels of IGFBP-4, a structurally related protein, or glyceraldehyde-3-phosphate dehydrogenase, a housekeeping gene. Knock-down of IGFBP-5 resulted in a significant increase in the number of transferase-mediated dUTP nick end labeling-positive cells and a decrease in a bone differentiation parameter (alkaline phosphatase activity) but had little effect on basal or insulin-like growth factor I-induced proliferation. Overexpression of a siRNA-resistant IGFBP-5 mutant in the IGFBP-5 knock-down cells restored the levels of survival to the control level; overexpression of IGFBP-4 or wild type IGFBP-5 had no such effect. Paradoxically, the addition of exogenous IGFBP-5 not only failed to rescue IGFBP-5 knock-down-induced apoptosis, it caused a further increase in apoptosis. Furthermore, the addition of exogenous IGFBP-5 alone increased apoptosis. This pro-apoptotic action of exogenous IGFBP-5 was abolished when IGF-I was added in excess, suggesting that exogenous IGFBP-5 increases apoptosis by binding to and inhibiting the activities of insulin-like growth factors. These results indicate that endogenous and exogenous IGFBP-5 exhibits opposing biological actions on cell survival and underscore the necessity and utility of studying IGFBP functions through loss-of-function approaches.

Mass Spectrometric Analysis of Posttranslational Modifications of a Carrot Extracellular Glycoprotein

Expression of extracellular dermal glycoprotein (EDGP) is induced by biotic or abiotic stress. The amino acid sequence alignment showed that EDGP shared significant homology with proteins from legumes, tomato, Arabidopsis, wheat, and cotton. These proteins are involved in signal transduction or stress response systems. Most of the Cys residues in these proteins are conserved, suggesting that they share similar tertiary structures. Surface plasmon resonance (SPR) analysis shows that EDGP binds a soybean 4-kDa hormone-like peptide (4-kDa peptide) in vitro and reduction of EDGP decreased significantly the binding activity, implying that posttranslational modifications are important for its function. Therefore, we investigated the posttranslational modifications in EDGP using mass spectrometry. As the result, six disulfide bonds in EDGP were identified: Cys(70)-Cys(158), Cys(84)-Cys(89), Cys(97)-Cys(113), Cys(100)-Cys(108), Cys(201)-Cys(426), and Cys(332)-Cys(378). In addition, the N-terminal glutamine was cyclized into pyroglutamic acid. All four putative glycosylation sites were occupied by N-linked glycans, which have similar masses of m/z 1171. Finally, measuring the mass of the native protein showed that the posttranslational modifications of EDGP (pI 9.5) involved only disulfide bonds, N-terminal modification, and glycosylation.

High levels of 150-kDa insulin-like growth factor binding protein three ternary complex in patients with acromegaly and the effect of pegvisomant-induced serum IGF-I normalization

OBJECTIVE

To assess the effect of pegvisomant-induced serum insulin-like growth factor 1 (IGF-1) normalization on IGF binding proteins 1, 2, 3 (IGFBP-1, IGFBP-2 and IGFBP-3), total, non-bound (45 kDa) and 150-kDa ternary complex-associated IGFBP-3, and in vivo IGFBP-3 proteolysis in patients with active acromegaly.

DESIGN

The above parameters were measured in 16 patients (median age 57 (range 27-78)) with active acromegaly (serum IGF-I at least 30% above the upper limit of an age-related reference range after washout) in a paired manner on samples obtained after washout and the first occurrence of serum IGF-I normalization during pegvisomant therapy (median dose 15 mg/day (10-40 mg)).

RESULTS

Total IGFBP-3 and 150-kDa ternary complex-associated IGFBP-3 were significantly elevated in patients at baseline compared to controls ((mean+/-SEM) 4345+/-194 vs. 3456+/-159 microg/L, P<0.01 and 3908+/-160 va. 3042+/-149 microg/L, P<0.01, respectively), but no significant difference in 45-kDa IGFBP-3 or in vivo IGFBP-3 proteolysis was observed. Serum IGF-I normalization (699+/-76 to 242+/-28 microg/L, P<0.0001) was associated with a fall in total IGFBP-3 (4345+/-194 to 3283+/-160 microg/L, P<0.001) due to a reduction in 150-kDa ternary complex-associated IGFBP-3 (3908+/-160 to 3008+/-140 microg/L, P<0.0001). 45 kDa IGFBP-3 and in vivo IGFBP-3 proteolysis were unaffected by GH receptor blockade (326+/-13 to 330+/-18 microg/L, P=0.86; 30+/-3.5 to 30+/-3.9%, P=0.75, respectively).

CONCLUSIONS

GH receptor blockade in patients with acromegaly lowers IGF-I and 150-kDa IGFBP-3 ternary complex formation. 50 kDa ternary complex formation (not in vivo IGFBP-3 proteolysis) is GH dependent and measurement of 150-kDa ternary complex-associated IGFBP-3 may provide useful information regarding treatment efficacy in patients with acromegaly.

Evaluation of serum insulin-like growth factor binding proteins (IGFBP) in Angus cattle divergently selected for serum IGF-I concentration

Postweaning serum insulin-like growth factor-I (IGF-I) concentrations and serum IGF binding proteins (IGFBP) were investigated in 68 (1992 Fall-born) and 84 (1999 Fall-born) Angus cattle selected for either high or low serum IGF-I concentrations since 1989. Relative serum levels of IGFBP were determined by [125I]IGF-I Western ligand blotting. IGFBP species of 38-42, 34, 30, and 24 kDa were identified. The 34 kDa species was identified as IGFBP-2 by immunoblot analysis. No significant line effects were observed for any of the IGFBP. In both 1992 and 1999, heifers had higher IGFBP-2 levels than bulls (P<0.0005). In 1992 calves, relative levels of the 38-42 and 24 kDa species were significantly correlated with serum IGF-I concentration. In 1999 calves, none of the IGFBP were correlated with serum IGF-I, although IGFBP-2 was negatively correlated with several measures of body weight. No significant line effects were observed for growth or serum IGF-I traits in 1992 calves. However, 1999 high line calves had higher serum IGF-I concentrations and body weights than low line calves (P<0.05). In both 1992 and 1999 calves, bulls had higher serum IGF-I concentrations and body weights than heifers (P<0.05). Thus, while selection for high versus low serum IGF-I concentrations has resulted in divergence between the selection lines and also in changes in body weights, it has not resulted in changes in serum IGFBP levels. Furthermore, circulating IGFBP-2 appears to be higher in heifers than in bulls, and also appears to be negatively correlated with body weights.

Identification of relaxin-3/INSL7 as an endogenous ligand for the orphan G-protein-coupled receptor GPCR135

GPCR135, publicly known as somatostatin- and angiotensin-like peptide receptor, is expressed in the central nervous system and its cognate ligand(s) has not been identified. We have found that both rat and porcine brain extracts stimulated 35S-labeled guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) incorporation in cells over-expressing GPCR135. Multiple rounds of extraction, purification, followed by N-terminal sequence analysis of the ligand from porcine brain revealed that the ligand is a product of the recently identified gene, relaxin-3 (aka insulin-7 or INSL7). Recombinant human relaxin-3 potently stimulates GTPgammaS binding and inhibits cAMP accumulation in GPCR135 overexpressing cells with EC50 values of 0.25 and 0.35 nM, respectively. 125I-Relaxin-3 binds GPCR135 at high affinity with a Kd value of 0.31 nM. Relaxin-3 is the only member of the insulin/relaxin superfamily that can activate GPCR135. In situ hybridization showed that relaxin-3 mRNA is predominantly expressed in the dorsomedial ventral tegmental nucleus of the brainstem (aka nucleus incertus), as well as in discrete cells in the lateral periaqueductal gray and in the central gray nucleus. GPCR135 is expressed abundantly in the hypothalamus with discrete expression in the paraventricular nucleus of the hypothalamus and supraoptic nucleus, as well as in the cortex, septal nucleus, and preoptical area. Relaxin-3 has previously been shown to bind and activate the LGR7 relaxin receptor. However, we believe that neuroanatomical colocalization of GPCR135 and relaxin-3, coupled with a clear high affinity interaction, suggest that GPCR135 is the receptor for relaxin-3. The identification of relaxin-3 as the ligand for GPCR135 provides the framework for the discovery of a new brainstem/hypothalamus circuitry.

Modification of serum IGF-I, IGFBPs and SHBG levels by different HRT regimens

During the menopause, levels of SHBG, IGF-I and IGFBPs are significantly modified by the use of different HRT regimens.

OBJECTIVE

The aim of this study is to evaluate the influence of three different HRT regimens on serum levels of SHBG, IGF-I, IGFBP-1 and IGFBP-3 in postmenopausal women.

METHODS

41 postmenopausal women requesting HRT were enrolled in the study. Subjects were divided in three groups according to the therapy assigned; Group A: estradiol 2 mg/day+cyproterone acetate 1 mg/day in a cyclic sequential regimen; Group B: estradiol hemihydrate 2 mg/day plus norethisterone acetate (NETA) 1 mg/day in a continuous combined regimen; Group C: estradiol hemihydrate 1 mg/day plus NETA 0.5 mg/day in a continuous combined regimen. Blood samples were drawn before the start of hormonal treatment and after 6 months of HRT. Levels of SHBG, IGF-I, IGFBP-1 and IGFBP-3 in the serum were measured by means of a specific immunoassay.

RESULTS

In group A, a significant increase of SHBG, no change of IGFBPs and a significant decrease of IGF-I were observed; in group B and in group C, no significant variations for any of the parameters were recorded.

CONCLUSIONS

The association of cyproterone acetate to oral estradiol determines a significant reduction of IGF-I levels and an increase of SHBG; nevertheless, it does not seem to influence the serum levels of the IGF-I binding proteins. The treatment with oral continuous combined estrogens plus androgenic progestins, at low doses, produces minor, not significant, changes in the circulating levels of IGF-I, SHBG and IGFBPs.

6,7-dihydroxyisoquinoline-3-carboxylic acids are potent inhibitors on the binding of insulin-like growth factor (IGF) to IGF-binding proteins: optimization of the 1-position benzoyl side chain

A series of 1-benzoyl isoquinolines, based on compound 1, was synthesized and evaluated for their ability to displace IGF-I from its complex with IGF-binding protein-3. Successful modifications of 1 included the replacement of the 3,4-dihydroxybenzoyl group with a substituted benzyl group. These alternations culminated in the discovery of compounds such as 7o which had excellent in vitro potency (K(i)=9.4 nM) but with one less of the labile catechol functionality of 1.

Quinoline-carboxylic acids are potent inhibitors that inhibit the binding of insulin-like growth factor (IGF) to IGF-binding proteins

4-benzylquinolines 5, based on a series of isoquinolines 1, were prepared and tested as inhibitors of the IGF/IGFBP-3 complex based on their ability to displace IGF-I from its binding to IGF-binding protein-3. SAR studies on the 6,7-dihydroxy moiety of the quinoline 5a showed that the catecol moiety could be replaced with other functional groups. Computational modeling of the 5a/mini-IGFBP-5 complex revealed the possible binding site of 5a on IGFBP-5.

Diabetic neuropathy and nerve regeneration

Diabetic neuropathy is the most common peripheral neuropathy in western countries. Although every effort has been made to clarify the pathogenic mechanism of diabetic neuropathy, thereby devising its ideal therapeutic drugs, neither convinced hypotheses nor unequivocally effective drugs have been established. In view of the pathologic basis for the treatment of diabetic neuropathy, it is important to enhance nerve regeneration as well as prevent nerve degeneration. Nerve regeneration or sprouting in diabetes may occur not only in the nerve trunk but also in the dermis and around dorsal root ganglion neurons, thereby being implicated in the generation of pain sensation. Thus, inadequate nerve regeneration unequivocally contributes to the pathophysiologic mechanism of diabetic neuropathy. In this context, the research on nerve regeneration in diabetes should be more accelerated. Indeed, nerve regenerative capacity has been shown to be decreased in diabetic patients as well as in diabetic animals. Disturbed nerve regeneration in diabetes has been ascribed at least in part to all or some of decreased levels of neurotrophic factors, decreased expression of their receptors, altered cellular signal pathways and/or abnormal expression of cell adhesion molecules, although the mechanisms of their changes remain almost unclear. In addition to their steady-state changes in diabetes, nerve injury induces injury-specific changes in individual neurotrophic factors, their receptors and their intracellular signal pathways, which are closely linked with altered neuronal function, varying from neuronal survival and neurite extension/nerve regeneration to apoptosis. Although it is essential to clarify those changes for understanding the mechanism of disturbed nerve regeneration in diabetes, very few data are now available. Rationally accepted replacement therapy with neurotrophic factors has not provided any success in treating diabetic neuropathy. Aside from adverse effects of those factors, more rigorous consideration for their delivery system may be needed for any possible success. Although conventional therapeutic drugs like aldose reductase (AR) inhibitors and vasodilators have been shown to enhance nerve regeneration, their efficacy should be strictly evaluated with respect to nerve regenerative capacity. For this purpose, especially clinically, skin biopsy, by which cutaneous nerve pathology including nerve regeneration can be morphometrically evaluated, might be a safe and useful examination.

Insulin-like growth factor binding protein-5 (IGFBP-5) induces premature cell death in the mammary glands of transgenic mice

We have previously demonstrated that IGFBP-5 production by mammary epithelial cells increases dramatically during involution of the mammary gland. To demonstrate a causal relationship between IGFBP-5 and cell death we created transgenic mice expressing IGFBP-5 in the mammary gland using a mammary-specific promoter, β-lactoglobulin. DNA content in the mammary glands of transgenic mice was decreased as early as day 10 of pregnancy. Histological analysis indicated reduced numbers of alveolar end buds, with decreased ductal branching. Transgenic dams produced IGFBP-5 in their milk at concentrations similar to those achieved at the end of normal lactation. Mammary cell number and milk synthesis were both decreased by approximately 50% during the first 10 days of lactation. BrdU labelling was decreased, whereas DNA ladders were increased in transgenic animals on day 1 of lactation. On day 2 postpartum, the epithelial invasion of the mammary fat pad was clearly impaired in transgenic animals. The concentrations of the pro-apoptotic molecule caspase-3 and of plasmin were both increased in transgenic animals whilst the concentrations of 2 prosurvival molecules Bcl-2 and Bcl-xLwere both decreased. In order to examine whether IGFBP-5 acts by inhibiting the survival effect of IGF-I we examined IGF receptor phosphorylation and Akt phosphorylation and showed that both were inhibited. We attempted to “rescue” the transgenic phenotype by using growth hormone to increase endogenous IGF-I concentrations or by implanting minipumps delivering an IGF-1 analogue, R3-IGF-1, which binds weakly to IGFBP-5. Growth hormone treatment failed to affect mammary development suggesting that increased concentrations of endogenous IGF-1 are insufficient to overcome the high concentrations of IGFBP-5 produced by these transgenic animals. In contrast mammary development (gland weight and DNA content) was normalised by R3-IGF-I although milk production was only partially restored. This is the first demonstration that over-expression of IGFBP-5 can lead to; impaired mammary development, increased expression of the pro-apoptotic molecule caspase-3, increased plasmin generation and decreased expression of pro-survival molecules of the Bcl-2 family. It clearly demonstrates that IGF-I is an important developmental/survival factor for the mammary gland and, furthermore, this cell death programme may be utilised in a wide variety of tissues.

Regulation of granulosa cell-derived insulin-like growth factor binding proteins (IGFBPs): role for protein kinase-C in the pre- and posttranslational modulation of IGFBP-4 and IGFBP-5

A growing body of information suggests antigonadotropic and atretogenic roles for granulosa cell-derived insulin-like growth factor binding proteins (IGFBPs) 4 and 5 during ovarian folliculogenesis. Activation of protein kinase-A (PKA) in rat granulosa cells has been shown to modulate the relative expression of IGFBP-4 and -5 transcripts and proteins. In this article, we assess the role of protein kinase-C (PKC) in this regard. Provision of granulosa cells with phorbol 12-myristate 13-acetate (PMA) (but not 4alphaPMA, an inert analogue), a tumor-promoting phorbol ester and an established activator of PKC, was without significant effect on the expression of IGFBP-4 transcripts but resulted in biphasic dose-dependent alterations in IGFBP-5 transcripts and in the accumulation of the IGFBP-4 and -5 proteins. Comparable effects were noted for GnRH, an established PKC agonist. Provision of staurosporine, a potent inhibitor of the catalytic subunit of PKC, produced significant dose-dependent decrements in the relative expression of IGFBP-5 transcripts. Treatment with FSH (presumptively PKA-mediated) markedly attenuated the ability of PMA or GnRH to upregulate the accumulation of the IGFBP-5 (but not IGFBP-4) protein. Taken together, our present findings indicate that the modulation of rat ovarian IGFBP-4 and -5 is PKC as well as PKA dependent and that these two signaling pathways interact in a diametrically opposed and antagonistic fashion.

The role of protein kinase C-delta in PTH stimulation of IGF-binding protein-5 mRNA in UMR-106-01 cells

We have investigated the role of protein kinase C (PKC) signal transduction pathways in parathyroid hormone (PTH) regulation of insulin-like growth factor-binding protein-5 (IGFBP-5) gene expression in the rat osteoblast-like cell line UMR-106-01. Involvement of the PKC pathway was determined by the findings that bisindolylmaleimide I inhibited 40% of the PTH effect, and 1 microM bovine PTH-(3-34) stimulated a 10-fold induction of IGFBP-5 mRNA. PTH-(1-34) and PTH-(3-34) (100 nM) both stimulated PKC-delta translocation from the membrane to the nuclear fraction. Rottlerin, a PKC-delta-specific inhibitor, and a dominant negative mutant of PKC-delta were both able to significantly inhibit PTH-(1-34) and PTH-(3-34) induction of IGFBP-5 mRNA, suggesting a stimulatory role for PKC-delta in the effects of PTH. Phorbol 12-myristate 13-acetate (PMA) stimulated PKC-alpha translocation from the cytosol to the membrane and inhibited approximately 50% of the PTH-(1-34), forskolin, and 8-bromoadenosine 3',5'-cyclic monophosphate-stimulated IGFBP-5 mRNA levels, suggesting that PKC-alpha negatively regulates protein kinase A (PKA)-mediated induction of IGFBP-5 mRNA. These results suggest that the induction of IGFBP-5 by PTH is both PKA and PKC dependent and PKC-delta is the primary mediator of the effects of PTH via the PKC pathway.

Use of mutagenesis to probe IGF-binding protein structure/function relationships

The IGF-binding proteins (IGFBPs) are multifunctional proteins that modulate IGF actions. To determine whether specific domains within these proteins account for specific functions, we and other laboratories have used in vitro mutagenesis. Prior experiments that used a variety of techniques had identified discrete regions within each protein that were proposed to account for specific functions. Alterations of these regions by substituting charged residues with neutral residues or hydrophobic residues with nonhydrophobic residues as well as domain swapping, i.e., substituting a domain from one specific form of IGFBP for the homologous domain in another form, has resulted in the elucidation of the functions of many of these specific sequences. Because the areas of protein sequence that are altered involve a limited number of amino acids, they generally do not alter the conformation of the entire protein; therefore, these specific substitutions can often be correlated with the functional changes that occur after mutagenesis. Mutants have been particularly useful for performing functional analyses in which the purified mutant protein is added to a biological test system. In some cases it has been possible to overexpress the mutagenized protein and determine whether the constitutively synthesized, mutant form of IGFBP has altered functional activity. These results have revealed that discrete regions of IGFBP sequence can mediate important and specific functional properties of these proteins.

Discovery of a series of nonpeptide small molecules that inhibit the binding of insulin-like growth factor (IGF) to IGF-binding proteins

Insulin-like growth factors (IGF-I and II) play an important role in metabolic and mitogenic activities through stimulation of the IGF-I receptor on the cell surface. Although the concentration of IGF in blood and cerebrospinal fluid is quite high (>100 nM), this large pool of IGF is biologically inactive because of its association with six distinct binding proteins, which form high-affinity complexes with IGF. Thus, inhibitors of IGF-binding proteins (IGFBPs), especially IGFBP-3, could potentially alter the distribution between the "free" and "bound" forms of IGF and thereby elevate biologically active IGF-I to exert a beneficial effect on those patients with diseases that respond to the application of exogenous IGF-I. Whereas IGF-I peptide variants, which bind to IGFBPs but not the IGF-I receptor, have been shown to be potent IGF/IGFBP inhibitors, small molecule nonpeptide IGF/IGFBP inhibitors have the potential advantages of oral bioavailability and flexible dosing regimen. Here we report the discovery of several isoquinoline analogues, exemplified by 1 and 2, which bind IGFBP-3 as well as other IGFBPs at low nanomolar concentrations. More importantly, both compounds were shown to be able to release biologically active IGF-I from the IGF-I/IGFBP-3 complex. These results point to the feasibility of developing orally active therapeutics to treat IGF-responsive diseases by optimization of the lead molecules 1 and 2.

Identification of a nonpeptide ligand that releases bioactive insulin-like growth factor-I from its binding protein complex

Insulin-like growth factor-I (IGF-I) has both metabolic and mitogenic activities mediated through interaction with the type 1 IGF receptor. The circulation of IGF-I in blood and interstitial fluid is not free but bound mostly to a family of six high affinity IGF-binding proteins, which form stable complexes with IGF and neutralize its bioactivity. Therefore, displacement of this large pool of endogenous IGF from the binding proteins could elevate "free" IGF levels to elicit beneficial effects in diabetes and other IGF-responsive diseases comparable with those produced by administration of exogenous IGF-I. We report here the identification of a nonpeptide ligand NBI-31772, which displaces IGF-I from all six IGF-binding proteins at low nanomolar concentrations from screening of the in-house chemical libraries. Furthermore, the released free IGF-I was shown to be biologically active in an in vitro bioassay. Thus, NBI-31772 could serve as a valuable lead molecule for the design of novel therapeutics to treat diabetes and other IGF-responsive diseases.

Insulin-like growth factor binding proteins in femoral and vertebral bone marrow stromal cells: expression and regulation by thyroid hormone and dexamethasone

Insulin-like growth factor (IGF)-I is an important regulator of bone metabolism. Clinical observations suggest that different anatomic sites within the adult skeleton respond differently to hormonal and therapeutic treatment, and recent studies on bone marrow stromal cells in culture show that there are skeletal site-dependent differences in the gene expression of IGF-I. The actions of IGF-I and -II on bone cells are known to be modulated by the IGF binding proteins (IGFBP)-1 through -6 and the Type I and Type II IGF receptors. Therefore, we compared the expression of IGFBP-1 through -6 in adult female rat bone marrow stromal cell cultures derived from two separate skeletal sites: vertebrae and femurs. The cultures were maintained simultaneously under conditions that support osteoblast differentiation from osteoprogenitors present in the femoral and vertebral marrow cell populations. We also addressed whether IGFBP messenger RNA levels are regulated by thyroid hormone (T(3)) and dexamethasone (dex) treatment in femoral vs. vertebral marrow stromal cells in vitro, since steroid hormones play an important role in skeletal function. Northern blot analyses revealed that there are distinct skeletal site differences in the gene expression of IGFBPs. The vertebral marrow cultures express IGFBP-2 through -6 mRNAs, with IGFBP-2, IGFBP-4, and IGFBP-6 mRNAs predominating. The femoral marrow stromal cell cultures express only IGFBP-4 and IGFBP-6. Importantly, vertebral marrow cultures have much higher IGFBP mRNA steady-state levels than femoral cultures for all the detected IGFBP transcripts. IGFBP-1 is not detected in either femoral or vertebral cultures. In addition to a skeletal site difference, we show that T(3) and dex regulate the expression of specific IGFBP mRNAs. T(3) treatment also upregulates IGF-I protein secretion by vertebral marrow stromal cell cultures. Interestingly, the type I receptor for IGF-I was expressed equivalently in cultures from the two skeletal sites. These findings have important implications for the anatomical site specificities of hormonal responses that are noted in the skeleton.

A new radioimmunoassay to measure rat insulin-like growth factor binding protein-4 (IGFBP-4) in serum, wound fluid and conditioned media

Insulin-like growth factor binding protein-4 (IGFBP-4) is, like the other five IGFBPs, a critical regulator of the activity of insulin-like growth factor-I (IGF-I) and IGF-II. Because of the possible role of IGFBP-4 in multiple systems including reproduction, pregnancy, bone formation and wound healing, we developed a radioimmunoassay (RIA) to measure the concentration of IGFBP-4 in the serum, extracellular fluid and conditioned media of cells of rodents so that these animal models could be better exploited. Rat IGFBP-4 was expressed in Escherichia coli and purified to homogeneity. The recombinant material was used to raise a rabbit polyclonal antibody against rat IGFBP-4 and for iodination and standards. The RIA developed was sensitive to less than 1 ng/mL of rat IGFBP-4 and IGF-I did not interfere. There was no cross-reactivity with other rat IGFBPs on immuno-Western analysis of serum and wound fluid. IGFBP-4 from mouse serum did cross-react in our assay; however, serum from horse, pig or human showed no cross-reaction. Human IGFBP-1 and IGFBP-3 showed a very weak cross-reactivity. Serum IGFBP-4 levels showed no gender difference but did reveal a significant 66% increase in older rats. During the course of wound healing, which is IGF-I dependent, IGFBP-4 showed no changes. In conclusion an RIA for rat IGFBP-4 has been developed that specifically measures the concentration of IGFBP-4 in the sera, extracellular fluid and conditioned media of rodents. With this assay, the role of IGFBP-4 and IGFs in growth, development and the function of multiple systems can be further investigated using rodent models.

Insulin-like growth factor binding protein 5 and type-1 insulin-like growth factor receptor are differentially regulated during apoptosis in cerebellar granule cells

Neuronal apoptosis is considered to play a significant role in several neuropathological conditions. However, the molecular mechanisms underlying neuronal apoptosis are poorly understood. Insulin-like growth factor (IGF) signalling is considered to be an important regulator of neuronal differentiation, survival and apoptosis. We have examined the expression of two members of the IGF system, insulin-like growth factor binding protein 5 (IGFBP-5) and the type-1 IGF receptor (IGF1R), during apoptosis of rat cerebellar granule cells (CGCs) in vitro. We describe a prominent downregulation of IGFBP-5 mRNA and protein expression. We also show that IGF-I increases IGFBP-5 expression in CGCs and that the downregulation of IGFBP-5 mRNA can be suppressed by inhibiting mRNA synthesis with actinomycin D. The expression of IGF1R mRNA showed a transient upregulation during potassium chloride (KCl) deprivation induced apoptosis, in contrast to the IGF1R protein level, which was downregulated during KCl deprivation. Our results provide insight into the expression of IGF-related genes during neuronal apoptosis, and indicate that they mediate a protective response to the withdrawal of trophic stimulation. It seems that the expression of IGFBP-5 and IGF1R is regulated to maximize the availability of IGF and the activity of IGF-triggered survival signalling.

Selective alterations in organ sizes in mice with a targeted disruption of the insulin-like growth factor binding protein-2 gene

Insulin-like growth factor binding protein 2 (IGFBP-2) is one member of the family of IGF binding proteins believed to have both endocrine functions elicited by modulating serum IGF half-life and transport as well as autocrine/paracrine functions that result from blocking or enhancing the availability of IGFs to bind cell surface receptors. To clarify the in vivo role of IGFBP-2, we have used gene targeting to introduce a null IGFBP-2 allele into the mouse genome. Animals homozygous for the altered allele are viable and fertile, contain no IGFBP-2 mRNA, and have no detectable IGFBP-2 in the adult circulation. Heterozygous and homozygous animals showed no significant differences in prenatal or postnatal body growth. Analyses of organ weights in adult males, however, revealed that spleen weight was reduced and liver weight was increased in the absence of IGFBP-2. In addition, ligand blot analyses of sera from adult IGFBP-2 null males showed that IGFBP-1, IGFBP-3, and IGFBP-4 levels were increased relative to wild-type mice. These results demonstrate that up-regulation of multiple IGFBPs accompanies the absence of IGFBP-2 and that IGFBP-2 has a critical role, either directly or indirectly, in modulating spleen and liver size.

Regulation of insulin-like growth factor binding protein-5 mRNA abundance in rat intestinal smooth muscle

IGF-I increases abundance of IGFBP-5 mRNA in rat intestinal smooth muscle cells (RISM), and IGFBP-5 protein in RISM conditioned media. The translational blocker, cycloheximide, decreased the abundance of IGFBP-5 mRNA to undetectable levels, suggesting that IGFBP-5 mRNA integrity is linked to protein synthesis. We studied the mechanism of IGF-I's effect on IGFBP-5 mRNA, and the role of cytoplasmic proteins in modulating IGFBP-5 mRNA abundance. Anisomycin, emetine, and puromycin abolished IGFBP-5 mRNA as seen with cycloheximide. Cycloheximide had a dose- and time-dependent effect on IGFBP-5 mRNA. IGF-I increased IGFBP-5 nuclear transcripts by reverse transcription-polymerase chain reaction (RT-PCR), suggesting that IGF-I acts at least partially by increasing IGFBP-5 mRNA transcription. Protein synthesis inhibitors did not affect IGFBP-5 nuclear transcripts, therefore, they affect only mature mRNA. The IGFBP-5 mRNA 3' and 5' UTRs were cloned and their sequences searched for adenosine-uridine rich elements (AUREs), elements shown to regulate RNA stability. RNA mobility gel shift assay showed two protein activities that bind to nt 922 to 2076 of the 3' UTR, a region that contains an AURE. One protein activity (BA2) was decreased in cytoplasmic extracts from cycloheximide-treated RISM. These data demonstrate that IGFBP-5 mRNA integrity is dependent on protein synthesis. The 3' UTR of IGFBP-5 contains elements shown to bind proteins important for RNA stability regulation. This region binds RISM cytoplasmic proteins, and may mediate the dramatic effect of cycloheximide on IGFBP-5 abundance. RNA-protein interactions may be important to IGFBP-5 mRNA stability and ultimately, to IGFBP-5 actions.

Vascular endothelial growth factor and transforming growth factor-beta1 regulate the expression of insulin-like growth factor-binding protein-3, -4, and -5 in large vessel endothelial cells

We investigated the effect of diabetes-associated growth factors on the expression of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGFBPs) in cultured endothelial cells from bovine aorta. Gene expression was measured by solution hybridization, and proteins were measured by enzyme-linked immunosorbent assay, RIA, or Western blot. The cells expressed messenger RNA (mRNA) for IGFBP-2 through -6 and IGFBP-2 through -5 proteins were detected in conditioned medium. Vascular endothelial growth factor inhibited IGFBP-3 mRNA (P < 0.01) and protein expression and increased IGFBP-5 mRNA (P < 0.001) and protein. Transforming growth factor-beta1 inhibited IGFBP-3 (P < 0.01), IGFBP-4 (P < 0.01), and IGF-I mRNA expression, whereas at the protein level only IGFBP-3 was significantly decreased. IGF-I, insulin, or angiotensin II did not affect IGF-I or IGFBP mRNA expression. At the protein level, IGF-I clearly increased IGFBP-5 levels in conditioned medium. In conclusion, vascular endothelial growth factor and transforming growth factor-beta1 regulate IGFBP expression in bovine aortic endothelial cells. These observations provide a new aspect of regulation for the IGF-system in macrovascular endothelium, with possible implications for subendothelial smooth muscle cells and development of diabetic angiopathy.