Regulation of insulin-like growth factor-I (IGF-I) delivery by IGF binding proteins and receptors

Effects of IGF-1 on the Cardiovascular System

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Cardiovascular (CV) diseases are the most common health problems worldwide, with a permanent increase in incidence. Growing evidence underlines that insulin-like growth factor 1 (IGF-1) is a very important hormone responsible for normal CV system physiology. IGF-1 is an anabolic growth hormone, responsible for cell growth, differentiation, proliferation, and survival. Despite systemic effects, IGF-1 exerts a wide array of influences in the CV system affecting metabolic homeostasis, vasorelaxation, cardiac contractility and hypertrophy, autophagy, apoptosis, and antioxidative processes. The vasodilatory effect of IGF-1, is achieved through the regulation of the activity of endothelial nitric oxide synthase (eNOS) and, at least partly, through enhancing inducible NOS (iNOS) activity. Also, IGF-1 stimulates vascular relaxation through regulation of sodium/potassiumadenosine- triphosphatase. Numerous animal studies provided evidence of diverse influences of IGF-1 in the CV system such as vasorelaxation, anti-apoptotic and prosurvival effects. Human studies indicate that low serum levels of free or total IGF-1 contribute to an increased risk of CV and cerebrovascular disease. Large human trials aiming at finding clinical efficacy and outcome of IGF-1-related therapy are of great interest.

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We look forward to the development of new IGF 1 therapies with minor side effects. In this review, we discuss the latest literature data regarding the function of IGF-1 in the CV system in the physiological and pathophysiological conditions.

MODEL-BASED ANALYSIS OF IGF-1 EFFECT ON OSTEOBLAST AND OSTEOCLAST REGULATION IN BONE TURNOVER

The main determinant of bone Ca accretion is a bimolecular regulatory network on osteoblast (OB) and osteoclast (OC). Even though IGF-1 is known as an important regulator in bone cell cycle, little has been done to model IGF-1 action in bone cell regulation. Thus, the objective is to develop a mathematical model that depicts the regulatory action of IGF-1 onto the OB and OC interaction, and to evaluate adolescent and adult bone Ca accretion in response to differences in IGF-1 levels. As a result, a dynamic model of OB and OC with two main regulatory systems, i.e., Receptor Activator for Nuclear Factor [Formula: see text]B (RANK)-RANK Ligand (RANKL)-osteoprogerin (OPG) system, and TGF-[Formula: see text], was augmented with the IGF-1, and incorporated into Ca kinetic data to predict exchangeable bone Ca. The developed model could predict a change in OB and OC levels in response to perturbations in regulators, producing results consistent with bone physiology and published experimental data. The model also estimated parametric difference in regulators between adults and adolescents, suggesting that RANKL/OPG in adolescents was about 4 times higher than in adults, while adolescent serum PTH and IGF-1 concentrations were 60% and 220% of those of adults, respectively. This study highlighted the influence of IGF-1 on the regulation of bone cells in positively modulating bone Ca, suggesting that IGF-1 may be an effective target for reducing bone loss by promoting mature OB.

Effects of Tobacco Smoking on the Degeneration of the Intervertebral Disc: A Finite Element Study

Tobacco smoking is associated with numerous pathological conditions. Compelling experimental evidence associates smoking to the degeneration of the intervertebral disc (IVD). In particular, it has been shown that nicotine down-regulates both the proliferation rate and glycosaminoglycan (GAG) biosynthesis of disc cells. Moreover, tobacco smoking causes the constriction of the vascular network surrounding the IVD, thus reducing the exchange of nutrients and anabolic agents from the blood vessels to the disc. It has been hypothesized that both nicotine presence in the IVD and the reduced solute exchange are responsible for the degeneration of the disc due to tobacco smoking, but their effects on tissue homeostasis have never been quantified. In this study, a previously presented computational model describing the homeostasis of the IVD was deployed to investigate the effects of impaired solute supply and nicotine-mediated down-regulation of cell proliferation and biosynthetic activity on the health of the disc. We found that the nicotine-mediated down-regulation of cell anabolism mostly affected the GAG concentration at the cartilage endplate, reducing it up to 65% of the value attained in normal physiological conditions. In contrast, the reduction of solutes exchange between blood vessels and disc tissue mostly affected the nucleus pulposus, whose cell density and GAG levels were reduced up to 50% of their normal physiological levels. The effectiveness of quitting smoking on the regeneration of a degenerated IVD was also investigated, and showed to have limited benefit on the health of the disc. A cell-based therapy in conjunction with smoke cessation provided significant improvements in disc health, suggesting that, besides quitting smoking, additional treatments should be implemented in the attempt to recover the health of an IVD degenerated by tobacco smoking.

Simulation predicts IGFBP2-HIF1α interaction drives glioblastoma growth

Tremendous strides have been made in improving patients’ survival from cancer with one glaring exception: brain cancer. Glioblastoma is the most common, aggressive and highly malignant type of primary brain tumor. The average overall survival remains less than 1 year. Notably, cancer patients with obesity and diabetes have worse outcomes and accelerated progression of glioblastoma. The root cause of this accelerated progression has been hypothesized to involve the insulin signaling pathway. However, while the process of invasive glioblastoma progression has been extensively studied macroscopically, it has not yet been well characterized with regards to intracellular insulin signaling. In this study we connect for the first time microscale insulin signaling activity with macroscale glioblastoma growth through the use of computational modeling. Results of the model suggest a novel observation: feedback from IGFBP2 to HIF1α is integral to the sustained growth of glioblastoma. Our study suggests that downstream signaling from IGFI to HIF1α, which has been the target of many insulin signaling drugs in clinical trials, plays a smaller role in overall tumor growth. These predictions strongly suggest redirecting the focus of glioma drug candidates on controlling the feedback between IGFBP2 and HIF1α.

Current treatment for glioblastoma patients is limited to nonspecific methods: surgery followed by a combination of radio- and chemotherapy. With these methods, glioma patient survival is less than one year post-diagnosis. Targeting specific protein signaling pathways offers potentially more potent therapies. One promising potential target is the insulin signaling pathway, which is known to contribute to glioblastoma progression. However, drugs targeting this pathway have shown mixed results in clinical trials, and the detailed mechanisms of how the insulin signaling pathway promotes glioblastoma growth remain to be elucidated. Here, we developed a computational model of insulin signaling in glioblastoma in order to study this pathway’s role in tumor progression. Using the model, we systematically test contributions of different insulin signaling protein interactions on glioblastoma growth. Our model highlights a key driver for the growth of glioblastoma: IGFBP2-HIF1α feedback. This interaction provides a target that could open the door for new therapies in glioma and other solid tumors.

A computational analysis on the implications of age-related changes in the expression of cellular signals on the role of IGF-1 in intervertebral disc homeostasis

Insulin-like growth factor-1 (IGF-1) is a well-known anabolic agent in intervertebral discs (IVD), promoting both proteoglycan (PG) biosynthesis and cell proliferation. Accordingly, it is believed that IGF-1 plays a central role in IVD homeostasis. The IGF-mediated anabolic activity in IVD occurs when the growth factor, free from binding proteins (IGFBP), binds to IGF cell surface receptors (IGF-1R). Previous studies reported that, with aging, cellular expression of IGFBP increases, while that of IGF-1R decreases. Both changes in cellular signals are thought to be among the factors that are responsible for the age-related decline in IGF-mediated PG biosynthesis, which ultimately leads to disc degeneration. In this study, a computational model describing the role of IGF-1 in the homeostasis of IVD was deployed in a parametric analysis to investigate the effects of age-related changes in expression of IGF-1R and IGFBP on the IGF-mediated upregulation of PG biosynthesis and cellular proliferation. It was found that changes in the expression of IGF-1R and IGFBP mostly affected the nucleus pulposus, while in the most external disc regions (annulus fibrosus and cartilage endplates) the IVD homeostatic balance was unaltered. It was shown that a decrease of IGF-1R expression caused reduction of both PG levels and cell density in the tissue. In contrast, increase in IGFBP expression increased both PG and cell concentration, suggesting that such change in cellular signaling may be a plausible defense mechanism from age-related IVD degeneration.

Modeling the role of IGF-1 on extracellular matrix biosynthesis and cellularity in intervertebral disc

The insulin-like growth factor-1 (IGF-1) is a well-known anabolic agent for intervertebral disc (IVD), promoting both proteoglycan (PG) biosynthesis and cell proliferation. Accordingly, it is believed that IGF-1 may play a central role in IVD homeostasis. Furthermore, the exogenous administration of IGF-1 has been proposed as a possible therapeutic strategy for disc degeneration. The objectives of this study were to develop a new computational framework for describing the mechanisms regulating IGF-mediated homeostasis in IVD, and to apply this numerical tool for investigating the effectiveness of exogenous administration of IGF-1 for curing disc degeneration. A diffusive-reactive model was developed for describing competitive binding of IGF-1 to its binding proteins and cell surface receptors, with the latter reaction initiating the intracellular signaling mechanism leading to PG production and cell proliferation. Because PG production increases cell metabolic rate, and cell proliferation increases nutritional demand, nutrients transport and metabolism were also included into the model, and co-regulated, together with IGF-1, IVD cellularity. The sustainability and the effectiveness of IGF-mediated anabolism were investigated for conditions of pathologically insufficient nutrient supply, and for the case of exogenous administration of IGF-1 to degenerated IVD. Results showed that pathological nutrients deprivation, by decreasing cellularity, caused a reduction of PG biosynthesis. Also, exogenous administration of IGF-1 was only beneficial in well-nourished regions of IVD, and exacerbated cell mortality in malnourished regions. These findings remark the central role of nutrition in IVD health, and suggest that adequate nutritional supply is paramount for achieving a successful IGF-based therapy for disc degeneration.

Altered mechano-chemical environment in hip articular cartilage: effect of obesity

The production of extracellular matrix (ECM) components of articular cartilage is regulated, among other factors, by an intercellular signaling mechanism mediated by the interaction of cell surface receptors (CSR) with insulin-like growth factor-1 (IGF-1). In ECM, the presence of binding proteins (IGFBP) hinders IGF-1 delivery to CSR. It has been reported that levels of IGF-1 and IGFBP in obese population are, respectively, lower and higher than those found in normal population. In this study, an experimental-numerical approach was adopted to quantify the effect of this metabolic alteration found in obese population on the homeostasis of femoral hip cartilage. A new computational model, based on the mechano-electrochemical mixture theory, was developed to describe competitive binding kinetics of IGF-1 with IGFBP and CSR, and associated glycosaminoglycan (GAG) biosynthesis. Moreover, a gait analysis was carried out on obese and normal subjects to experimentally characterize mechanical loads on hip cartilage during walking. This information was deployed into the model to account for effects of physiologically relevant tissue deformation on GAG production in ECM. Numerical simulations were performed to compare GAG biosynthesis in femoral hip cartilage of normal and obese subjects. Results indicated that the lower ratio of IGF-1 to IGFBP found in obese population reduces cartilage GAG concentration up to 18 % when compared to normal population. Moreover, moderate physical activity, such as walking, has a modest beneficial effect on GAG production. The findings of this study suggest that IGF-1/IGFBP metabolic unbalance should be accounted for when considering the association of obesity with hip osteoarthritis.

Modeling the Insulin-Like Growth Factor System in Articular Cartilage

IGF signaling is involved in cell proliferation, differentiation and apoptosis in a wide range of tissues, both normal and diseased, and so IGF-IR has been the focus of intense interest as a promising drug target. In this computational study on cartilage, we focus on two questions: (i) what are the key factors influencing IGF-IR complex formation, and (ii) how might cells regulate IGF-IR complex formation? We develop a reaction-diffusion computational model of the IGF system involving twenty three parameters. A series of parametric and sensitivity studies are used to identify the key factors influencing IGF signaling. From the model we predict the free IGF and IGF-IR complex concentrations throughout the tissue. We estimate the degradation half-lives of free IGF-I and IGFBPs in normal cartilage to be 20 and 100 mins respectively, and conclude that regulation of the IGF half-life, either directly or indirectly via extracellular matrix IGF-BP protease concentrations, are two critical factors governing the IGF-IR complex formation in the cartilage. Further we find that cellular regulation of IGF-II production, the IGF-IIR concentration and its clearance rate, all significantly influence IGF signaling. It is likely that negative feedback processes via regulation of these factors tune IGF signaling within a tissue, which may help explain the recent failures of single target drug therapies aimed at modifying IGF signaling.

High glucose-mediated alterations of mechanisms important in myogenesis of mouse C2C12 myoblasts

We have examined the progression and regulation of myogenesis, cellular levels of IGFBP-4, -5, -6, and several extracellular matrix (ECM) proteins (fibronectin, integrin α5, β1 subunits and a disintegrin metalloprotease ADAM12) in murine C2C12 myoblasts during 3-day differentiation under high glucose alone or combined with high insulin, factors characteristic for type 1 and 2 diabetes. High ambient glucose inhibited myogenesis of C2C12 myoblasts, an effect manifested by a twofold decrease in myoblast fusion, a drop in intracellular MyoD, myogenin and MHC levels, and increased cellular content of active myostatin isoform. Reduction in myogenesis by high glucose is accompanied by increase in cellular levels of IGFBP-4 and -6 and decrease in IGFBP-5. High glucose could modify ECM components assembly, by the increase in fibronectin levels and the decrease in metalloprotease ADAM12, without the effect on integrin α5 and β1 subunits. In contrast, high glucose and high insulin activate myoblast differentiation, manifested by an increase in fusion index and myogenin, as well as a drop in myostatin levels. The presence of high insulin prevented high-glucose-dependent changes in IGFBPs and ECM proteins. The data indicate the potential mechanisms of the influence of extracellular environment associated with maternal diabetes and insulin resistance on foetal myogenesis.

Uptake, efflux, and mass transfer coefficient of fluorescent PAMAM dendrimers into pancreatic cancer cells

Targeted delivery of imaging agents to cells can be optimized with the understanding of uptake and efflux rates. Cellular uptake of macromolecules is studied frequently with fluorescent probes. We hypothesized that the internalization and efflux of fluorescently labeled macromolecules into and out of mammalian cells could be quantified by confocal microscopy to determine the rate of uptake and efflux, from which the mass transfer coefficient is calculated. The cellular influx and efflux of a third generation poly(amido amine) (PAMAM) dendrimer labeled with an Alexa Fluor 555 dye was measured in Capan-1 pancreatic cancer cells using confocal fluorescence microscopy. The Capan-1 cells were also labeled with 5-chloromethylfluorescein diacetate (CMFDA) green cell tracker dye to delineate cellular boundaries. A dilution curve of the fluorescently labeled PAMAM dendrimer enabled quantification of the concentration of dendrimer in the cell. A simple mass transfer model described the uptake and efflux behavior of the PAMAM dendrimer. The effective mass transfer coefficient was found to be 0.054±0.043μm/min, which corresponds to a rate constant of 0.035±0.023min(-1) for uptake of the PAMAM dendrimer into the Capan-1 cells. The effective mass transfer coefficient was shown to predict the efflux behavior of the PAMAM dendrimer from the cell if the fraction of labeled dendrimer undergoing non-specific binding is accounted for. This work introduces a novel method to quantify the mass transfer behavior of fluorescently labeled macromolecules into mammalian cells.

Insulin-like growth factors promote vasculogenesis in embryonic stem cells

The ability of embryonic stem cells to differentiate into endothelium and form functional blood vessels has been well established and can potentially be harnessed for therapeutic angiogenesis. However, after almost two decades of investigation in this field, limited knowledge exists for directing endothelial differentiation. A better understanding of the cellular mechanisms regulating vasculogenesis is required for the development of embryonic stem cell-based models and therapies. In this study, we elucidated the mechanistic role of insulin-like growth factors (IGF1 and 2) and IGF receptors (IGFR1 and 2) in endothelial differentiation using an embryonic stem cell embryoid body model. Both IGF1 or IGF2 predisposed embryonic stem to differentiate towards a mesodermal lineage, the endothelial precursor germ layer, as well as increased the generation of significantly more endothelial cells at later stages. Inhibition of IGFR1 signaling using neutralizing antibody or a pharmacological inhibitor, picropodophyllin, significantly reduced IGF-induced mesoderm and endothelial precursor cell formation. We confirmed that IGF-IGFR1 signaling stabilizes HIF1α and leads to up-regulation of VEGF during vasculogenesis in embryoid bodies. Understanding the mechanisms that are critical for vasculogenesis in various models will bring us one step closer to enabling cell based therapies for neovascularization.

Minireview: Putting physiology back into estrogens' mechanism of action

After decades of research, the mechanism by which estrogens stimulate the proliferation of epithelial cells in the endometrium and mammary gland, and in the carcinomas that arise in those tissues, is still not understood. Cells do not proliferate in response to 17β-estradiol (E2) alone, and although it is widely recognized that growth factors play a role in E2's proliferative effect, exactly how they are involved is unclear. It has long been known that the proliferation of endometrial epithelial cells is preceded by dramatic increases in blood flow and microvascular permeability, filling the subepithelial stroma with plasma and the proteins it contains, such as IGF-I, which is known to synergize with E2 in the induction of cell proliferation. The hyperpermeability is caused by vascular endothelial growth factor (VEGF), which is rapidly induced by E2, via the transcription factors hypoxia-inducible factor 1 and estrogen receptor α, in luminal epithelial cells in vivo. As we recently showed, VEGF is also strongly induced in endometrial cancer cells in vitro when excessive degradation of hypoxia-inducible factor 1α, caused by the abnormally high oxygen level to which cultured cells are exposed, is prevented. Putting these facts together, we now propose a new model of E2-induced proliferation in which VEGF-induced vascular hyperpermeability plays an essential role. E2 first induces the expression by endometrial epithelial cells of VEGF, which then acts in a paracrine manner to induce interendothelial cell gaps in subepithelial blood vessels, through which plasma and the proteins therein enter the adjacent stroma. Plasma carries even more E2, which circulates bound to proteins, and IGF-l, which together drive epithelial cells completely through the cell cycle.

Growth factor and cytokine interactions in myogenesis. Part II. Expression of IGF binding proteins and protein kinases essential for myogenesis in mouse C2C12 myogenic cells exposed to TNF-α and IFN-γ

The aim of the study was to examine potential interactions among IGF-I and proinflammatory cytokines, TNF-α and IFN-γ, in the regulation of local IGF-I bioavailability and cellular proteins mediating myogenic signals. We investigated levels of IGFBP-4, -5, -6, protein kinase Czeta (PKCζ), p38 and extracellular signal-regulated kinase (ERK1/2) in differentiating mouse C2C12 myoblasts. IGF-I significantly stimulated expression of IGFBP-5. TNF-α and IFN-γ attenuated the expression of IGFBP-4 and -6 under basal conditions and in the presence of IGF-I, and inhibited IGF-I-induced IGFBP-5 expression during 5-day myogenesis. TNF-α and IFN-γ markedly attenuated p38 expression in the presence of IGF-I on the 5th day of myogenesis. When combined with IGF-I the cytokines exerted opposite effects on the PKCζ level, i.e. TNF-α caused an increase, whereas IFN-γ reduced the cellular content of this kinase. Exposition of C2C12 myoblasts to IGF-I or cytokines led to the stimulation of ERK1/2 phosphorylation; however, both TNF-α and IFN-γ exerted an inhibitory effect on the activation of ERK1/2 in myoblasts cultured in the presence of IGF-I. We concluded as follows: i) TNF-α and IFN-γ present in the extracellular environment of differentiating C2C12 myoblasts can alter the local bioavailability of IGF-I by inhibiting the expression of IGFBP-4, -5, and -6, ii) the decrease in p38 expression and ERK1/2 phosphorylation in C2C12 myoblasts exposed to cytokines can lead to disturbances in IGF-I-regulated myogenesis.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

In vivo oocyte developmental competence is reduced in lean but not in obese superovulated dairy cows after intraovarian administration of IGF1

The present study investigated the role of IGF1 in lactating lean and non-lactating obese dairy cows by injecting 1 μg IGF1 into the ovaries prior to superovulation. This amount of IGF1 has been linked with pregnancy loss in women with the polycystic ovary syndrome (PCOS) and was associated with impaired bovine oocyte competence in vitro. Transcript abundance and protein expression of selected genes involved in apoptosis, glucose metabolism, and the IGF system were analyzed. Plasma concentrations of IGF1 and leptin, and IGF1 in uterine luminal fluid (ULF), were also measured. IGF1 treatment decreased embryo viability in lean cows to the levels observed in obese cows. Obese cows were not affected by IGF1 treatment and showed elevated levels of IGF1 (in both plasma and ULF) and leptin. Blastocysts from lean cows treated with IGF1 showed a higher abundance of SLC2A1 and IGFBP3 transcripts. IGF1 treatment reduced protein expression of tumor protein 53 in blastocysts of lean cows, whereas the opposite was observed in obese cows. IGF1 in plasma and ULF was correlated only in the control groups. Blastocyst transcript abundance of IGF1 receptor and IGFBP3 correlated positively with IGF1 concentrations in both plasma and ULF in lean cows. The detrimental microenvironment created by IGF1 injection in lean cows and the lack of effect in obese cows resemble to a certain extent the situation observed in PCOS patients, where IGF1 bioavailability is increased in normal-weight women but reduced in obese women, suggesting that this bovine model could be useful for studying IGF1 involvement in PCOS.

Acute regulation of IGF-I by alterations in post-exercise macronutrients

This investigation sought to examine the contributions of exercise and nutrient replenishment on in vivo regulation of the insulin-like growth factor-I (IGF-I) axis components. Eight college-aged males completed three high-intensity interval training (HIIT) protocols followed by three post-exercise nutritional protocols: (1) placebo (EX); (2) carbohydrate only (CHO); and (3) essential amino acid/carbohydrate (EAA/CHO). Samples were analyzed for growth hormone (GH), free IGF-I, IGFBP-1, IGFBP-2, insulin, hematocrit, hemoglobin, serum leucine, matrix metalloproteinase-9 (MMP-9) proteolytic activity, and presence of IGFBP-3 protease activity. No evidence for IGFBP-3 proteolysis was observed. Significant increases in [free IGF-I] and [leucine] were observed in the EAA/CHO group only. Significant differences were noted in [IGFBP-1] and [IGFBP-2] across conditions. Significant increases in [GH] and MMP-9 activity were observed in all groups. These results indicate that post-exercise macronutrient ratio is a determinant of [free IGF-I], [IGFBP-1 and -2] and may play a role in modulating the IGF-I axis in vivo.

Physiologically based pharmacokinetics of molecular imaging nanoparticles for mRNA detection determined in tumor-bearing mice

Disease detection and management might benefit from external imaging of disease gene mRNAs. Previously we designed molecular imaging nanoparticles (MINs) based on peptide nucleic acids complementary to cancer gene mRNAs. The MINs included contrast agents and analogs of insulin-like growth factor 1 (IGF-1). Analysis of MIN tumor uptake data showed stronger binding in tumors than in surrounding tissues. We hypothesized that MINs with an IGF-1 analog stay in circulation by binding to IGF-binding proteins. To test that hypothesis, we fit the tissue distribution results of several MINs in xenograft-bearing mice to a physiological pharmacokinetics model. Fitting experimental tissue distribution data to model-predicted mass transfer of MINs from blood into organs and tumors converged only when the parameter for MINs bound to circulating IGF-binding proteins was set to 10%-20% of the injected MIN dose. This result suggests that previous mouse imaging trials used more MINs than necessary. This prediction can be tested by a ramp of decreasing doses.

Estrogen rapidly activates the PI3K/AKT pathway and hypoxia-inducible factor 1 and induces vascular endothelial growth factor A expression in luminal epithelial cells of the rat uterus

We have previously shown that 17beta-estradiol (E(2)) increases vascular endothelial growth factor A (Vegfa) gene expression in the rat uterus, resulting in increased microvascular permeability, and that this involves the simultaneous recruitment of hypoxia-inducible factor 1 (HIF1) and estrogen receptor alpha (ESR1) to the Vegfa gene promoter. Both events require the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. However, those studies were carried out using whole uterine tissue, and while most evidence indicates that the likely site of E(2)-induced Vegfa expression is luminal epithelial (LE) cells, other studies have identified stromal cells as the site of that expression. To address this question, the pathway regulating Vegfa expression was reexamined using LE cells rapidly isolated after E(2) treatment. In addition, we further characterized the nature of the receptor through which E(2) triggers the signaling events that lead to Vegfa expression using the specific ESR1 antagonist ICI 182,780. In agreement with previous results in the whole uterus, E(2) stimulated Vegfa mRNA expression in LE cells, peaking at 1 h (4- to 14-fold) and returning to basal levels by 4 h. Treatment with E(2) also increased phosphorylation of AKT in LE cells, as well as of the downstream mediators FRAP1 (mTOR), GSK3B, and MDM2. The alpha subunit of HIF1 (HIF1A) was present in LE cells before E(2) treatment, was unchanged 1 h after E(2), but was >2-fold higher by 4 h. Chromatin immunoprecipitation analysis showed that HIF1A was recruited to the Vegfa promoter by 1 h and was absent again by 4 h. The E(2) activation of the PI3K/AKT pathway, HIF1A recruitment to the Vegfa promoter, and Vegfa expression were all blocked by ICI 182,780. In summary, the rapid E(2)-induced signaling events that lead to the expression of Vegfa observed previously using the whole uterus occur in LE cells and appear to be initiated via a membrane form of ESR1.

Endometrial expression of the insulin-like growth factor system during uterine involution in the postpartum dairy cow

Rapid uterine involution in the postpartum period of dairy cows is important to achieve a short interval to conception. Expression patterns for members of the insulin-like growth factor (IGF) family were determined by in situ hybridisation at day 14+/-0.4 postpartum (n=12 cows) to investigate a potential role for IGFs in modulating uterine involution. Expression in each uterine tissue region was measured as optical density units and data were analysed according to region and horn. IGF-I mRNA was localized to the sub-epithelial stroma (SES) of inter-caruncular and caruncular endometrium. Both IGF-II and IGF-1R expression was detected in the deep endometrial stroma (DES), the caruncular stroma and myometrium. IGFBP-2, IGFBP-4 and IGFBP-6 mRNAs were all localised to the SES of inter-caruncular and caruncular uterine tissue, and in the DES and caruncular stroma, with IGFBP-4 mRNA additionally expressed in myometrium. IGFBP-3 mRNA was only detectable in luminal epithelium. IGFBP-5 mRNA was found in myometrium, inter-caruncular and caruncular SES and caruncular stroma. These data support a role for IGF-I and IGF-II in the extensive tissue remodelling and repair which the postpartum uterus undergoes to return to its non-pregnant state. The differential expression of binding proteins between tissues (IGFBP-3 in epithelium, IGFBP-2, -4, -5 and -6 in stroma and IGFBP-4 and -5 in myometrium) suggest tight control of IGF activity within each compartment. Differential expression of many members of the IGF family between the significantly larger previously gravid horn and the previously non-gravid horn may relate to differences in their rate of tissue remodelling.

The role of IGF-I and its binding proteins in the development of type 2 diabetes and cardiovascular disease

Patients with insulin resistance and type 2 diabetes have an excessive risk of cardiovascular disease (CVD); this increased risk is not fully explained by traditional risk factors such as hypertension and dyslipidaemias. There is now compelling evidence to suggest that abnormalities of insulin-like growth factor-I (IGF-I) and one of its binding proteins, insulin-like growth factor-binding protein-1 (IGFBP-1), occur in insulin-resistant states and may be significant factors in the pathophysiology of CVD. We reviewed articles and relevant bibliographies following a systematic search of MEDLINE for English language articles between 1966 and the present, using an initial search strategy combining the MeSH terms: IGF, diabetes and CVD. Our aim was first to review the role of IGF-I in vascular homeostasis and to explore the mechanisms by which it may exert its effects. We also present an overview of the physiology of the IGF-binding proteins, and finally, we sought to summarize the evidence to date describing the changes in the insulin/IGF-I/IGFBP-1 axis that occur in type 2 diabetes and CVD; in particular, we have focused on the potential vasculoprotective effects of both IGF-I and IGFBP-1. We conclude that this system represents an interesting and novel therapeutic target in the prevention of CVD in type 2 diabetes.

Alginate Encapsulation Impacts the Insulin-like Growth Factor-I System of Monolayer-Expanded Equine Articular Chondrocytes and Cell Response to Interleukin-1β

Alginate hydrogel culture has been shown to reestablish chondrocytic phenotype following monolayer expansion; however, previous studies have not adequately addressed how culture conditions affect the signaling systems responsible for chondrocyte metabolic activity. Here we investigate whether chondrocyte culture history influences the insulin-like growth factor-I (IGF-I) signaling system and its regulation by interleukin-1 (IL-1). Articular chondrocytes (ACs) from equine stifle joints were expanded by serial passage and were either encapsulated in alginate beads or maintained in monolayer culture for 10 days. Alginate-derived cells (ADCs) and monolayer-derived cells (MDCs) were then plated at high density, stimulated with IL-1beta (1 and 10 ng/mL) or IGF-I (50 ng/mL) for 48 h, and assayed for levels of type I IGF receptor (IGF-IR), IGF binding proteins (IGFBPs), and endogenously secreted IGF-I. Intermediate alginate culture yielded relatively low IGF-IR levels that increased in response to IL-1beta, whereas higher receptor levels on MDCs were reduced by cytokine. MDCs also secreted substantially more IGFBP-2, the predominant binding protein in conditioned media (CM), though IL-1beta suppressed levels for both cell populations. Concentrations of autocrine/paracrine IGF-I paralleled IGFBP-2 secretion. Disparate basal levels of IGF-IR and IGFBP-2, but not IGF-I, were attributed to relative transcript expression. Systemic differences coincided with varied effects of IL-1beta and IGF-I on cell growth and type I collagen expression. We conclude that culture strategy impacts the IGF-I signaling system of ACs, potentially altering their capacity to mediate cartilage repair. Consideration of hormonal regulators may be an essential element to improve chondrocyte culture protocols used in tissue engineering applications.

The effect of cyclic deformation and solute binding on solute transport in cartilage

Diffusive transport must play an important role in transporting nutrients into cartilage due to its avascular nature. Recent theoretical studies generally support the idea that cyclic loading enhances large molecule transport through advection. However, to date, reactive transport, i.e. the effects of solute binding, has not yet been taken into consideration in cyclically deformed cartilage. In the present study, we develop a reactive transport model to describe the potential role of binding of solute within cyclically deformed cartilage. Our results show that binding does have a significant effect on transport, particularly for the low IGF-I concentrations typical of synovial fluid. A dynamic loading regime of high strain magnitudes (up to 10%) in combination with high frequencies (e.g. 1 Hz) was seen to produce the most dramatic results with enhanced total uptake ratio as high as 25% averaged over the first 5h of cyclic loading.

Transcriptional and proteolytic regulation of the insulin-like growth factor-I system of equine articular chondrocytes by recombinant equine interleukin-1beta

Interleukin-1 (IL-1) and insulin-like growth factor-I (IGF-I), which have opposing effects on matrix metabolism within articular cartilage, are thought to play prominent roles in the pathogenesis of osteoarthritis. To better understand the link between these anabolic (IGF-I) and catabolic (IL-1) stimuli, we examined exogenous IL-1 regulation of the IGF-I signaling system of articular chondrocytes (ACs). Equine ACs from non-arthritic stifle joints were expanded in monolayer culture, encapsulated for 10 days in alginate beads, and stimulated as high-density monolayers with recombinant equine IL-1beta (0, 1, 10 ng/ml) for 48 h. IL-1beta enhanced expression of IGF-IR levels, as determined by both [125I]-IGF-I binding studies and Western blotting, while reducing the concentration of endogenous IGF-I detected in conditioned media by radioimmunoassay. Western ligand blotting revealed that chondrocytes primarily secreted IGF binding proteins (IGFBPs) with molecular weights of 28-30 and 32-34 kDa, which were identified as IGFBPs 5 and 2, respectively, and that IL-1beta treatment diminished IGFBP-2, the prominent homolog in conditioned media. Northern blot analysis suggested IL-1beta regulation of IGF-I and, to some extent, IGF-IR was mediated by transcription; however, the cytokine did not affect IGFBP-2 expression. To test for evidence of proteolysis by matrix metalloproteinases (MMPs), additional cultures were co-incubated with inhibitors for MMPs 2/9, 3, and 8. IGFBP-2 suppression was partially reversed by gelatinase (MMP-2/9) inhibition. In summary, these findings further delineate the role of IL-1 as a key regulator of the IGF-I system within articular cartilage, demonstrating that regulation occurs through both direct (transcriptional) and indirect (proteolytic) mechanisms.

Enhanced insulin-like growth factor-I (IGF-I) cell association at reduced pH is dependent on IGF binding protein-3 (IGFBP-3) interaction

The cellular microenvironment impacts how signals are transduced by cells and plays a key role in tissue homeostasis. Although pH is generally well regulated, there are a number of situations where acidosis occurs and our work addresses how low pH impacts cell association of insulin-like growth factor-I (IGF-I) in the presence of IGF binding protein-3 (IGFBP-3). We have previously shown that IGF-I cell binding was enhanced in the presence of IGFBP-3 at low pH and now show that this binding is IGFBP-mediated as it is inhibited by Y60L-IGF-I, a mutant with reduced affinity for the IGF receptor (IGF-IR), and unaffected by insulin, which binds but not IGFBPs. Using surface plasmon resonance (SPR), we show that direct binding between IGF-I and IGFBP-3 is pH sensitive. Despite this, the key step in the process appears to be IGFBP-3 cell surface association as Long-R(3)-IGF-I, a mutant with reduced affinity for IGFBPs, shows a similar increase in cell association at pH 5.8 in the presence of IGFBP-3 but does not exhibit pH-dependent binding by SPR. Further, analysis indicates a large increase in low-affinity binding sites for IGF-I in the presence of IGFBP-3 and an elimination of IGF-I enhanced binding when a non-cell associating mutant of IGFBP-3 is added in place of IGFBP-3. That the IGFBP-3-mediated binding localizes IGF-I away from IGF-IR is suggested by triton-solubility testing and indicates additional complexities to IGF-I regulation by IGFBP-3. Identifying the pH-dependent binding partner(s) for IGFBP-3 is a necessary next step in deciphering this process.