Impact of hypoxia on IGF-I, IGF-II, IGFBP-3, ALS and IGFBP-1 regulation and on IGF1R gene expression in children

Muscle hypertrophy training does not suppress the GH/IGF axis in young adult males

PURPOSE

This study aimed to analyze the expression of the IGF type-1 receptor gene (IGF-1r) and IGF-I, GH, testosterone, and IGFBP-3 concentrations in young people subjected to 10 weeks of muscle hypertrophy training.

METHODS

IGF-1r expression, serum concentrations of IGF-I, IGFBP-3, GH, and total testosterone, as well as body composition, fat percentage, and body mass index, were determined for 22 healthy young males at three moments of resistance training (first, fifth, and tenth week of training).

RESULTS

Throughout the 10 weeks of training, a reduction was observed in the relative expression of the IGF-1r gene (2-ΔΔCT) and an increase in IGF-I and GH concentrations. A reduction in total testosterone concentrations was detected during the recovery period in the fifth week. The IGFBP-3 concentrations did not change throughout the training.

CONCLUSIONS

The resistance training protocol prescribed for muscle hypertrophy did not suppress the GH-IGF-I axis, but it did cause alterations in IGF-1r gene expression and in IGF-I kinetics compatible with increased IGF bioactivity.

Generation of hyaline-like cartilage tissue from human mesenchymal stromal cells within the self-generated extracellular matrix

Chondrocytic hypertrophy, a phenotype not observed in healthy hyaline cartilage, is often concomitant with the chondrogenesis of human mesenchymal stromal cells (hMSCs). This undesired feature represents one of the major obstacles in applying hMSCs for hyaline cartilage repair. Previously, we developed a method to induce hMSC chondrogenesis within self-generated extracellular matrix (mECM), which formed a cartilage tissue with a lower hypertrophy level than conventional hMSC pellets. In this study, we aimed to test the utility of hypoxia and insulin-like growth factor-1 (IGF1) on further reducing hypertrophy. MSC-mECM constructs were first subjected to chondrogenic culture in normoxic or hypoxic (5%) conditions. The results indicated that hMSC-derived cartilage formed in hypoxic culture displayed a significantly reduced hypertrophy level than normoxic culture. However, hMSC chondrogenesis was also suppressed under hypoxic culture, partially due to the reduced activity of the IGF1 pathway. IGF1 was then supplemented in the chondrogenic medium, which promoted remarkable hMSC chondrogenesis under hypoxic culture. Interestingly, the IGF1-enhanced hMSC chondrogenesis, under hypoxic culture, was not at the expense of promoting significantly increased hypertrophy. Lastly, the cartilage tissues created by hMSCs with different conditions were implanted into osteochondral defect in rats. The results indicated that the tissue formed under hypoxic condition and induced with IGF1-supplemented chondrogenic medium displayed the best reparative results with minimal hypertrophy level. Our results demonstrate a new method to generate hyaline cartilage-like tissue from hMSCs without using exogenous scaffolds, which further pave the road for the clinical application of hMSC-based cartilage tissue engineering. STATEMENT OF SIGNIFICANCE: In this study, hyaline cartilage-like tissues were generated from human mesenchymal stromal cells (hMSCs), which displayed robust capacity in repairing the osteochondral defect in rats. In particular, the extracellular matrix created by hMSCs was used, so no exogenous scaffold was needed. Through a series of optimization, we defined that hypoxic culture and supplementation of insulin-like growth factor-1 (IGF-1) in chondrogenic medium resulted in robust cartilage formation with minimal hypertrophy. We also demonstrated that hypoxic culture suppressed chondrogenesis and hypertrophy through modulating the Wnt/β-catenin and IGF1 pathways, respectively. Our results demonstrate a new method to generate hyaline cartilage-like tissue from hMSCs without using exogenous scaffolds, which will further pave the road for the clinical application of hMSCs-based cartilage tissue engineering.

The steroid hormone ecdysone regulates growth rate in response to oxygen availability

In almost all animals, physiologically low oxygen (hypoxia) during development slows growth and reduces adult body size. The developmental mechanisms that determine growth under hypoxic conditions are, however, poorly understood. Here we show that the growth and body size response to moderate hypoxia (10% O₂) in Drosophila melanogaster is systemically regulated via the steroid hormone ecdysone. Hypoxia increases level of circulating ecdysone and inhibition of ecdysone synthesis ameliorates the negative effect of low oxygen on growth. We also show that the effect of ecdysone on growth under hypoxia is through suppression of the insulin/IGF-signaling pathway, via increased expression of the insulin-binding protein Imp-L2. These data indicate that growth suppression in hypoxic Drosophila larvae is accomplished by a systemic endocrine mechanism that overlaps with the mechanism that slows growth at low nutrition. This suggests the existence of growth-regulatory mechanisms that respond to general environmental perturbation rather than individual environmental factors.

IGF1 gene is epigenetically activated in preterm infants with intrauterine growth restriction

Background

IGF1 is a key molecule in the regulation of growth and metabolism. Low IGF1 secretion is known to cause growth restriction in childhood, as well as deregulated lipid metabolism, cardiovascular disease, and diabetes in adulthood. The IGF1 gene P2 promoter is highly methylated, resulting in low secretion of IGF1 in small infants and children. However, it is unknown when this methylation occurs. The aim of study was to clarify the point when this epigenetic program occurs during intrauterine development.

We analyzed 56 preterm infants born before 32 weeks of gestation, including 19 intrauterine growth restriction (IUGR) infants whose birth weights were lower than − 2SD calculated by the Japanese datasets. We extracted genomic DNA from whole blood at birth; methylation of the six CpG sites in the IGF1 P2 promoter was analyzed by the bisulfite amplicon method using the MiSeq platform.

Results

In contrast to term infants and children, the methylation of all six CpG sites positively correlated with body weight and body length at birth. IGF1 P2 promoter methylation levels were significantly reduced in all six CpG sites in infants with IUGR.

Conclusions

These findings indicated that the IGF1 gene is epigenetically activated before 32 weeks of gestation in infants with IUGR and that the activated gene may become suppressed after this time point. This study may provide new insights to prevent the onset of adult diseases and to aid in nutritional management for preterm birth infants in neonatal intensive care units.

IGF-1R mRNA expression is increased in obese children

OBJECTIVES

Obese children are often taller than age-matched subjects. Reports on GH and IGF-I levels in obese individuals are controversial, with normal and reduced GH-IGF-I levels having been reported in this group of patients. Thus, the aim of this study was to analyse insulin-like growth factor type 1 receptor (IGF-IR) mRNA expression in obese children.

METHODS

Forty-seven pre-pubertal children were included in this study: 29 were obese and taller than their target height, and 18 were normal eutrophic controls. Fasting blood samples were collected for IGF-IR mRNA expression in isolated lymphocytes and serum IGF-I, ALS, IGFBP-3, and IGFBP-1 concentration analysis.

RESULTS

Relative IGF-IR gene expression (2^-ΔΔCT) was significantly (P=0.025) higher in obese children (median 1.87) than in controls (1.15). Fourteen of the 29 obese subjects showed 2^-ΔΔCT values greater than or equal to 2, while only 2 individuals in the control group showed values above 2 (P=0.01). Obese children showed significantly (P=0.01) higher IGF-I concentrations than the control group (237ng/ml and 144ng/ml, respectively). Among obese patients, 65.5% had IGF-I values above the 75 percentile of the control group (P=0.02). ALS concentration was significantly (P=0.04) higher in the obese group, while IGFBP-3 levels were similar in obese and control children. IGFBP-1 concentration was lower in obese children, while insulin levels and HOMA-IR index were higher than in controls.

CONCLUSIONS

The higher IGF-IR mRNA expression observed in obese children, associated with the higher IGF-I and ALS and the lower IGFBP-1 levels, suggest that the higher stature observed in these children may be due to increased IGF-I bioactivity.

Insulin-Like Growth Factors in the Pathogenesis of Neurological Diseases in Children

Insulin-like growth factors play a key role for neuronal growth, differentiation, the survival of neurons and synaptic formation. The action of IGF-1 is most pronounced in the developing brain. In this paper we will try to give an answer to the following questions: Why are studies in children important? What clinical studies in neonatal asphyxia, infantile spasms, progressive encephalopathy-hypsarrhythmia-optical atrophy (PEHO) syndrome, infantile ceroid lipofuscinosis (INCL), autistic spectrum disorders (ASD) and subacute sclerosing encephalopathy (SSPE) have been carried out? What are IGF-based therapeutic strategies? What are the therapeutic approaches? We conclude that there are now great hopes for the therapeutic use of IGF-1 for some neurological disorders (particularly ASD).

Oxygen-sensitive regulation and neuroprotective effects of growth hormone-dependent growth factors during early postnatal development

Perinatal hypoxia severely disrupts metabolic and somatotrophic development, as well as cerebral maturational programs. Hypoxia-inducible transcription factors (HIFs) represent the most important endogenous adaptive mechanisms to hypoxia, activating a broad spectrum of growth factors that contribute to cell survival and energy homeostasis. To analyze effects of systemic hypoxia and growth hormone (GH) therapy (rhGH) on HIF-dependent growth factors during early postnatal development, we compared protein (using ELISA) and mRNA (using quantitative RT PCR) levels of growth factors in plasma and brain between normoxic and hypoxic mice (8% O2, 6 h; postnatal day 7, P7) at P14. Exposure to hypoxia led to reduced body weight ( P < 0.001) and length ( P < 0.04) compared with controls and was associated with significantly reduced plasma levels of mouse GH ( P < 0.01) and IGF-1 ( P < 0.01). RhGH abrogated these hypoxia-induced changes of the GH/IGF-1 axis associated with normalization of weight and length gain until P14 compared with controls. In addition, rhGH treatment increased cerebral IGF-1, IGF-2, IGFBP-2, and erythropoietin mRNA levels, resulting in significantly reduced apoptotic cell death in the hypoxic, developing mouse brain. These data indicate that rhGH may functionally restore hypoxia-induced systemic dysregulation of the GH/IGF-1 axis and induce upregulation of neuroprotective, HIF-dependent growth factors in the hypoxic developing brain.

Insulin-like growth factor 1 receptor-mediated cell survival in hypoxia depends on the promotion of autophagy via suppression of the PI3K/Akt/mTOR signaling pathway

Hypoxia is widely accepted as a fundamental biological phenomenon, which is strongly associated with tissue damage and cell viability under stress conditions. Insulin-like growth factor-1 (IGF-1) is known to protect tissues from multiple types of damage, and protect cells from apoptosis. Hypoxia is a regulatory factor of the IGF system, however the role of the IGF-1 receptor (IGF-1R) in hypoxia-induced apoptosis remains unclear. The present study investigated the potential mechanisms associated with IGF-1R-associated apoptosis under hypoxic conditions. Mouse embryonic fibroblasts exhibiting disruption or overexpression of IGF-1R (R- cells and R+ cells) were used to examine the level of apoptosis, autophagy, and production of reactive oxygen species (ROS). The autophagy inhibitor 3-methyladenine was used to assess the effect of autophagy on ROS production and apoptosis under hypoxic conditions. A potential downstream signaling pathway involving phosphatidylinositol 3-kinase (PI3K)/threonine protein kinase B (Akt)/mammalian target of rapamycin (mTOR) was identifiedby western blot analysis. The results demonstrated that hypoxia induced apoptosis, increased ROS production, and promoted autophagy in a time-dependent manner relative to that observed under normoxia. R+ cells exhibited a lower percentage of apoptotic cells, lower ROS production, and higher levels of autophagy when compared to that of R- cells. In addition, inhibition of autophagy led to increased ROS production and a higher percentage of apoptotic cells in the two cell types. Furthermore, IGF-1R is related with PI3K/Akt/mTOR signaling pathway and enhanced autophagy-associated protein expression, which was verified following treatment with the PI3K inhibitor LY294002. These results indicated that IGF-1R may increase cell viability under hypoxic conditions by promoting autophagy and scavenging ROS production, which is closed with PI3K/Akt/mTOR signaling pathway.

Intermittent Compressive Stress Enhanced Insulin-Like Growth Factor-1 Expression in Human Periodontal Ligament Cells

Mechanical force was shown to promote IGF-1 expression in periodontal ligament both in vitro and in vivo. Though the mechanism of this effect has not yet been proved, here we investigated the molecular mechanism of intermittent mechanical stress on IGF-1 expression. In addition, the role of hypoxia on the intermittent compressive stress on IGF-1 expression was also examined. In this study, human periodontal ligament cells (HPDLs) were stimulated with intermittent mechanical stress for 24 hours. IGF-1 expression was examined by real-time polymerase chain reaction. Chemical inhibitors were used to determine molecular mechanisms of these effects. For hypoxic mimic condition, the CoCl2 supplementation was employed. The results showed that intermittent mechanical stress dramatically increased IGF-1 expression at 24 h. The pretreatment with TGF-β receptor I or TGF-β1 antibody could inhibit the intermittent mechanical stress-induced IGF-1 expression. Moreover, the upregulation of TGF-β1 proteins was detected in intermittent mechanical stress treated group. Correspondingly, the IGF-1 expression was upregulated upon being treated with recombinant human TGF-β1. Further, the hypoxic mimic condition attenuated the intermittent mechanical stress and rhTGF-β1-induced IGF-1 expression. In summary, this study suggests intermittent mechanical stress-induced IGF-1 expression in HPDLs through TGF-β1 and this phenomenon could be inhibited in hypoxic mimic condition.

Endothelial activation and repair during hantavirus infection: association with disease outcome

Background.

 Endothelial activation and dysfunction play a central role in the pathogenesis of sepsis and viral hemorrhagic fevers. Hantaviral disease is a viral hemorrhagic fever and is characterized by capillary dysfunction, although the underlying mechanisms for hantaviral disease are not fully elucidated.

Methods.

 The temporal course of endothelial activation and repair were analyzed during Puumala hantavirus infection and associated with disease outcome and a marker for hypoxia, insulin-like growth factor binding protein 1 (IGFBP-1). The following endothelial activation markers were studied: endothelial glycocalyx degradation (syndecan-1) and leukocyte adhesion molecules (soluble vascular cellular adhesion molecule 1, intercellular adhesion molecule 1, and endothelial selectin). Cytokines associated with vascular repair were also analyzed (vascular endothelial growth factor, erythropoietin, angiopoietin, and stromal cell-derived factor 1).

Results.

 Most of the markers we studied were highest during the earliest phase of hantaviral disease and associated with clinical and laboratory surrogate markers for disease outcome. In particular, the marker for glycocalyx degradation, syndecan-1, was significantly associated with levels of thrombocytes, albumin, IGFBP-1, decreased blood pressure, and disease severity.

Conclusions.

 Hantaviral disease outcome was associated with endothelial dysfunction. Consequently, the endothelium warrants further investigation when designing future medical interventions.

Circulatory insulin-like growth factor-I and brain volumes in relation to neurodevelopmental outcome in very preterm infants

BACKGROUND

To evaluate the relationships between postnatal change in circulatory insulin-like growth factor-I (IGF-I) concentrations, brain volumes, and developmental outcome at 2 y of age in very preterm infants.

METHODS

IGF-I was measured weekly, and nutritional intake was calculated daily from birth until a postmenstrual age (PMA) of 35 wk. Individual β coefficients for IGF-I, IGF-I(B), representing the rate of increase in IGF-I from birth until a PMA of 35 wk were calculated. Brain magnetic resonance imaging was performed at term age, with segmentation into total brain, cerebellar, gray matter, and unmyelinated white matter volume (UWMV). Developmental outcome was evaluated using Bayley Scales of Infant Development-II.

RESULTS

Forty-nine infants, with mean gestational age (GA) of 26.0 wk, were evaluated at mean 24.6 mo corrected age. Higher IGF-I(B), UWMV, and cerebellar volume were associated with a decreased risk for a Mental Developmental Index (MDI) < 85 (odds ratio (95% confidence interval): 0.6 (0.4-0.9), 0.96 (0.94-0.99), and 0.78 (0.6-0.96), respectively). In multivariate analysis, higher IGF-I(B) and higher UWMV combined with female gender constituted the two models with the highest predictive value for MDI > 85.

CONCLUSION

A higher rate of increase in circulating IGF-I is associated with a decreased risk for subnormal MDI at 2 y of corrected age. This relationship is in part dependent on brain volume at term age.

Does adenotonsillectomy alter IGF-1 and ghrelin serum levels in children with adenotonsillar hypertrophy and failure to thrive? A prospective study

OBJECTIVES

Adenotonsillar hypertrophy (ATH) contributes to upper airway obstruction and recurrent tonsillitis in children. The aim of this study was to evaluate the effect of adenotonsillectomy on serum IGF-1 and ghrelin levels in children with ATH failure to thrive.

METHODS

Forty pre-pubertal children with more than 5 years of age (6.57 ± 1.284 years) suffering from ATH, sleep disorder breathing, snoring, open mouth breathing and growth retardation were studied. Blood samples were taken eight hours after fasting and weight and height were measured by SECA instrument. Blood samples were centrifuged immediately and the extracted sera were stored at -70 °C in Eppendorf vials. IGF-1 and ghrelin were measured by ELISA kit. Patients with adenotonsillectomy indication underwent adenotonsillectomy and serum levels of IGF-1 and ghrelin were measured 12 months after operation.

RESULTS

Weight, height and BMI were increased significantly after operation (P < 0.001). Serum IGF-1 and ghrelin levels increased significantly after operation compared to before operation (P < 0.001).

CONCLUSION

Growth retardation in children with adenotonsillar hypertrophy is related to lower serum IGF-1 levels. Ghrelin levels increase before the meals and ghrelin increases hunger and food intake. The results obtained from our study confirmed that weight, height and BMI increase significantly following adenotonsillectomy; this could in turns prevent undesirable and irreversible physiological changes that occur due to adenotonsillar hypertrophy. Adenotonsillectomy in children with adenotonsillar hypertrophy and failure to thrive increases IGF-1 and Ghrelin serum levels which might contribute to the improvement in the growth pattern of the children.