Insulin-like growth factor-binding protein-1 (IGFBP-1) mediates hypoxia-induced embryonic growth and developmental retardation

Genome-wide mapping of Hif-1α binding sites in zebrafish

Background

Hypoxia Inducible Factor (HIF) regulates a cascade of transcriptional events in response to decreased oxygenation, acting from the cellular to the physiological level. This response is evolutionarily conserved, allowing the use of zebrafish (Danio rerio) as a model for studying the hypoxic response. Activation of the hypoxic response can be achieved in zebrafish by homozygous null mutation of the von Hippel-Lindau (vhl) tumour suppressor gene. Previous work from our lab has focused on the phenotypic characterisation of this mutant, establishing the links between vhl mutation, the hypoxic response and cancer. To further develop fish as a model for studying hypoxic signalling, we examine the transcriptional profile of the vhl mutant with respect to Hif-1α. As our approach uses embryos consisting of many cell types, it has the potential to uncover additional HIF regulated genes that have escaped detection in analogous mammalian cell culture studies.

Results

We performed high-density oligonucleotide microarray analysis of the gene expression changes in von Hippel-Lindau mutant zebrafish, which identified up-regulation of well-known hypoxia response genes and down-regulation of genes primarily involved in lipid processing. To identify the dependency of these transcriptional changes on HIF, we undertook Chromatin Immunoprecipitation linked next generation sequencing (ChIP-seq) for the transcription factor Hypoxia Inducible Factor 1α (HIF-1α). We identified HIF-1α binding sites across the genome, with binding sites showing enrichment for an RCGTG motif, showing conservation with the mammalian hypoxia response element.

Conclusions

Transcriptome analysis of vhl mutant embryos detected activation of key hypoxia response genes seen in human cell models of hypoxia, but also suppression of many genes primarily involved in lipid processing. ChIP-seq analysis of Hif-1α binding sites unveiled an unprecedented number of loci, with a high proportion containing a canonical hypoxia response element. Whether these sites are functional remains unknown, nevertheless their frequent location near transcriptional start sites suggests functionality, and will allow for investigation into the potential hypoxic regulation of genes in their vicinity. We expect that our data will be an excellent starting point for analysis of both fish and mammalian gene regulation by HIF.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2169-x) contains supplementary material, which is available to authorized users.

Data Mining of Determinants of Intrauterine Growth Retardation Revisited Using Novel Algorithms Generating Semantic Maps and Prototypical Discriminating Variable Profiles

OBJECTIVES

Intra-uterine growth retardation is often of unknown origin, and is of great interest as a "Fetal Origin of Adult Disease" has been now well recognized. We built a benchmark based upon a previously analysed data set related to Intrauterine Growth Retardation with 46 subjects described by 14 variables, related with the insulin-like growth factor system and pro-inflammatory cytokines, namely interleukin-6 and tumor necrosis factor-α.

DESIGN AND METHODS

We used new algorithms for optimal information sorting based on the combination of two neural network algorithms: Auto-contractive Map and Activation and Competition System. Auto-Contractive Map spatializes the relationships among variables or records by constructing a suitable embedding space where 'closeness' among variables or records reflects accurately their associations. The Activation and Competition System algorithm instead works as a dynamic non linear associative memory on the weight matrices of other algorithms, and is able to produce a prototypical variable profile of a given target.

RESULTS

Classical statistical analysis, proved to be unable to distinguish intrauterine growth retardation from appropriate-for-gestational age (AGA) subjects due to the high non-linearity of underlying functions. Auto-contractive map succeeded in clustering and differentiating completely the conditions under study, while Activation and Competition System allowed to develop the profile of variables which discriminated the two conditions under study better than any other previous form of attempt. In particular, Activation and Competition System showed that ppropriateness for gestational age was explained by IGF-2 relative gene expression, and by IGFBP-2 and TNF-α placental contents. IUGR instead was explained by IGF-I, IGFBP-1, IGFBP-2 and IL-6 gene expression in placenta.

CONCLUSION

This further analysis provided further insight into the placental key-players of fetal growth within the insulin-like growth factor and cytokine systems. Our previous published analysis could identify only which variables were predictive of fetal growth in general, and identified only some relationships.

Exposure of clownfish larvae to suspended sediment levels found on the Great Barrier Reef: Impacts on gill structure and microbiome

Worldwide, increasing coastal development has played a major role in shaping coral reef species assemblages, but the mechanisms underpinning distribution patterns remain poorly understood. Recent research demonstrated delayed development in larval fishes exposed to suspended sediment, highlighting the need to further understand the interaction between suspended sediment as a stressor and energetically costly activities such as growth and development that are essential to support biological fitness. We examined the gill morphology and the gill microbiome in clownfish larvae (Amphiprion percula) exposed to suspended sediment concentrations (using Australian bentonite) commonly found on the inshore Great Barrier Reef. The gills of larvae exposed to 45 mg L(-1) of suspended sediment had excessive mucous discharge and growth of protective cell layers, resulting in a 56% thicker gill epithelium compared to fish from the control group. Further, we found a shift from 'healthy' to pathogenic bacterial communities on the gills, which could increase the disease susceptibility of larvae. The impact of suspended sediments on larval gills may represent an underlying mechanism behind the distribution patterns of fish assemblages. Our findings underscore the necessity for future coastal development to consider adverse effects of suspended sediments on fish recruitment, and consequently fish populations and ecosystem health.

Stunted by Developing in Hypoxia: Linking Comparative and Model Organism Studies

Animals develop in atmospheric hypoxia in a wide range of habitats, and tissues may experience O2 limitation of ATP production during postembryonic development if O2 supply structures do not keep pace with growing O2 demand during ontogeny. Most animal species are stunted by postembryonic development in hypoxia, showing reduced growth rates and size in moderate hypoxia (5-15 kPa Po2). In mammals, the critical Po2 that limits resting metabolic rate also falls in this same moderate hypoxic range, so stunted growth may simply be due to hypoxic limits on ATP production. However, in most invertebrates and at least some lower vertebrates, hypoxic stunting occurs at Po2 values well above those that limit resting metabolism. Studies with diverse model organisms have identified multiple homologous O2-sensing signaling pathways that can inhibit feeding and growth during moderate hypoxia. Together, these comparative and model organism-based studies suggest that hypoxic stunting of growth and size can occur as programmed inhibition of growth, often by inhibition of insulin stimulation of growth processes. Furthermore, there is increasing evidence that these same O2 signaling pathways can be utilized during normal animal development to ensure matching of O2 supply and demand structures and in mediation of variation in animal performance.

Chronic intermittent hypoxia is independently associated with reduced postoperative opioid consumption in bariatric patients suffering from sleep-disordered breathing

Background

Evidence suggests that recurrent nocturnal hypoxemia may affect pain response and/or the sensitivity to opioid analgesia. We tested the hypothesis that nocturnal hypoxemia, quantified by sleep time spent at an arterial saturation (SaO₂) < 90% and minimum nocturnal SaO₂ on polysomnography, are associated with decreased pain and reduced opioid consumption during the initial 72 postoperative hours in patients having laparoscopic bariatric surgery.

Methods

With Institutional Review Board approval, we examined the records of all patients who underwent laparoscopic bariatric surgery between 2004 and 2010 and had an available nocturnal polysomnography study. We assessed the relationships between the time-weighted average of pain score and total opioid consumption during the initial 72 postoperative hours, and: (a) the percentage of total sleep time spent at SaO₂ < 90%, (b) the minimum nocturnal SaO₂, and (c) the number of apnea/hypopnea episodes per hour of sleep. We used multivariable regression models to adjust for both clinical and sleep-related confounders.

Results

Two hundred eighteen patients were included in the analysis. Percentage of total sleep time spent at SaO₂ < 90% was inversely associated with total postoperative opioid consumption; a 5-%- absolute increase in the former would relatively decrease median opioid consumption by 16% (98.75% CI: 2% to 28%, P = 0.006). However, the percentage of total sleep time spent at SaO₂ < 90% was not associated with pain. The minimum nocturnal SaO₂ was associated neither with total postoperative opioid consumption nor with pain. In addition, neither pain nor total opioid consumption was significantly associated with the number of apnea/hypopnea episodes per hour of sleep.

Conclusions

Preoperative nocturnal intermittent hypoxia may enhance sensitivity to opioids.

Molecular Characterization and Expression Analysis of Insulin-like Growth Factor-1 and Insulin-like Growth Factor Binding Protein-1 Genes in Qinghai-Tibet Plateau Bos grunniens and Lowland Bos taurus

Insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-1 (IGFBP-1) play a pivotal role in regulating cellular hypoxic response. In this study, we cloned and characterized the genes encoding IGF-1 and IGFBP-1 to improve the current knowledge on their roles in highland Bos grunniens (Yak). We also compared their expression levels in the liver and kidney tissues between yaks and lowland cattle. We obtained full-length 465 bp IGF-1 and 792 bp IGFBP-1, encoding 154 amino acids (AA) IGF-1, and 263 AA IGFBP-1 protein, respectively using reverse transcriptase-polyerase chain reaction (RT-PCR) technology. Analysis of their corresponding amino acid sequences showed a high identity between B. grunniens and lowland mammals. Moreover, the two genes were proved to be widely distributed in the examined tissues through expression pattern analysis. Real-time PCR results revealed that IGF-1 expression was higher in the liver and kidney tissues in B. grunniens than in Bos taurus (p<0.05). The IGFBP-1 gene was expressed at a higher level in the liver (p<0.05) of B. taurus than B. grunniens, but it has a similar expression level in the kidneys of the two species. These results indicated that upregulated IGF-1 and downregulated IGFBP-1 are associated with hypoxia adaptive response in B. grunniens.

Exposure to prenatal smoking and early-life body composition: the healthy start study

OBJECTIVES

To examine associations between exposure to prenatal smoking and early-life changes in fat mass (FM), fat-free mass (FFM), and anthropometrics.

METHODS

About 670 mother-offspring pairs were analyzed in the longitudinal Healthy Start study. Maternal smoking data were collected during prenatal research visits. Offspring body composition and size were measured by air displacement plethysmography at delivery and postnatal follow-up (5 months) visits.

RESULTS

Comparing exposed and unexposed offspring, exposure to prenatal smoking was significantly associated with reduced neonatal FM (P = 0.007) and FFM (P = 0.02). In contrast, at 5 months, exposed offspring had comparable FM (P = 0.61) and FFM (P = 0.41). After subsequent adjustment for birth weight, offspring exposed to prenatal smoking had significantly greater FFM (154.7 g, 0.5, 309.0; P = 0.049) and sum of skinfolds (2.7 mm, 0.06, 5.3; P = 0.04). From delivery to follow-up, exposed offspring had significantly greater increases in FFM (156.4 g, 2.8, 310.1; P = 0.046) and sum of skinfolds (2.7 mm, 0.06, 5.3; P = 0.04), even after adjustment for respective delivery measures.

CONCLUSIONS

Exposure to prenatal smoking was significantly associated with rapid postnatal growth, which may increase the offspring's risk of metabolic diseases.

Molecular cloning and function analysis of insulin-like growth factor-binding protein 1a in blunt snout bream (Megalobrama amblycephala)

Insulin-like growth factor-binding protein 1 (IGFBP-1), a hypoxia-induced protein, is a member of the IGFBP family that regulates vertebrate growth and development. In this study, full-length IGFBP-1a cDNA was cloned from a hypoxia-sensitive Cyprinidae fish species, the blunt snout bream (Megalobrama amblycephala). IGFBP-1a was expressed in various organs of adult blunt snout bream, including strongly in the liver and weakly in the gonads. Under hypoxia, IGFBP-1a mRNA levels increased sharply in the skin, liver, kidney, spleen, intestine and heart tissues of juvenile blunt snout bream, but recovered to normal levels after 24-hour exposure to normal dissolved oxygen. In blunt snout bream embryos, IGFBP-1a mRNA was expressed at very low levels at both four and eight hours post-fertilization, and strongly at later stages. Embryonic growth and development rates decreased significantly in embryos injected with IGFBP-1a mRNA. The average body length of IGFBP-1a-overexpressed embryos was 82.4% of that of the control group, and somite numbers decreased to 85.2%. These findings suggest that hypoxia-induced IGFBP-1a may inhibit growth in this species under hypoxic conditions.

Hypoxia-inducible factor 2 alpha is essential for hepatic outgrowth and functions via the regulation of leg1 transcription in the zebrafish embryo

The liver plays a vital role in metabolism, detoxification, digestion, and the maintenance of homeostasis. During development, the vertebrate embryonic liver undergoes a series of morphogenic processes known as hepatogenesis. Hepatogenesis can be separated into three interrelated processes: endoderm specification, hepatoblast differentiation, and hepatic outgrowth. Throughout this process, signaling molecules and transcription factors initiate and regulate the coordination of cell proliferation, apoptosis, differentiation, intercellular adhesion, and cell migration. Hifs are already recognized to be essential in embryonic development, but their role in hepatogenesis remains unknown. Using the zebrafish embryo as a model organism, we report that the lack of Hif2-alpha but not Hif1-alpha blocks hepatic outgrowth. While Hif2-alpha is not involved in hepatoblast specification, this transcription factor regulates hepatocyte cell proliferation during hepatic outgrowth. Furthermore, we demonstrated that the lack of Hif2-alpha can reduce the expression of liver-enriched gene 1 (leg1), which encodes a secretory protein essential for hepatic outgrowth. Additionally, exogenous mRNA expression of leg1 can rescue the small liver phenotype of hif2-alpha morphants. We also showed that Hif2-alpha directly binds to the promoter region of leg1 to control leg1 expression. Interestingly, we discovered overrepresented, high-density Hif-binding sites in the potential upstream regulatory sequences of leg1 in teleosts but not in terrestrial mammals. We concluded that hif2-alpha is a key factor required for hepatic outgrowth and regulates leg1 expression in zebrafish embryos. We also proposed that the hif2-alpha-leg1 axis in liver development may have resulted from the adaptation of teleosts to their environment.

Identification of hypoxia-regulated genes in the liver of common sole (Solea solea) fed different dietary lipid contents

Coastal systems could be affected by hypoxic events brought about by global change. These areas are essential nursery habitats for several fish species including the common sole (Solea solea L.). Tolerance of fish to hypoxia depends on species and also on their physiological condition and nutritional status. Indeed, high dietary lipid content has been recently shown to negatively impact the resistance of sole to a severe hypoxic challenge. In order to study the molecular mechanisms involved in the early response to hypoxic stress, the present work examined the hepatic transcriptome in common sole fed diets with low and high lipid content, exposed to severe hypoxia. The activity of AMP-activated protein kinase (AMPK) was also investigated through the quantification of threonine-172 phosphorylation in the alpha subunit. The results show that hypoxia consistently regulates several actors involved in energy metabolism pathways and particularly AMPKα, as well as some involved in cell growth and maintenance or unfolded protein response. Our findings reveal that (1) the expression of genes involved in biological processes with high energy cost or implicated in aerobic ATP synthesis was down-regulated by hypoxia, contrary to genes involved in neoglucogenesis or in angiogenesis, (2) the consumption of high lipid induced regulation of metabolic pathways going against this energy saving, and (3) this control was fine-tuned by the regulation of several transcriptomic factors. These results provide insight into the biological processes involved in the hepatic response to hypoxic stress and underline the negative impact of high lipid consumption on the tolerance of common sole to hypoxia.

Hypoxia-inducible factor 3 is an oxygen-dependent transcription activator and regulates a distinct transcriptional response to hypoxia

Hypoxia-inducible factors (HIFs) play key roles in the cellular response to hypoxia. It is widely accepted that whereas HIF-1 and HIF-2 function as transcriptional activators, HIF-3 inhibits HIF-1/2α action. Contrary to this idea, we show that zebrafish Hif-3α has strong transactivation activity. Hif-3α is degraded under normoxia. Mutation of P393, P493, and L503 inhibits this oxygen-dependent degradation. Transcriptomics and chromatin immunoprecipitation analyses identify genes that are regulated by Hif-3α, Hif-1α, or both. Under hypoxia or when overexpressed, Hif-3α binds to its target gene promoters and upregulates their expression. Dominant-negative inhibition and knockdown of Hif-3α abolish hypoxia-induced Hif-3α-promoter binding and gene expression. Hif-3α not only mediates hypoxia-induced growth and developmental retardation but also possesses hypoxia-independent activities. Importantly, transactivation activity is conserved and human HIF-3α upregulates similar genes in human cells. These findings suggest that Hif-3 is an oxygen-dependent transcription factor and activates a distinct transcriptional response to hypoxia.

Neonatal IGF-1/IGFBP-1 axis and retinopathy of prematurity are associated with increased blood pressure in preterm children

Aim

Preterm children are at risk of developing increased blood pressure (BP). We evaluated possible associations between BP, early insulin-like growth factor-1 (IGF-1) and IGF-binding protein-1 (IGFBP-1) levels and retinopathy of prematurity (ROP) in preterm children.

Methods

The study included 32 infants: median gestational age 28.1 weeks (range 24.6–31.3) and birthweight standard deviation scores (SDS) (±SD) 1.0 ± 2.7. IGF-1 and IGFBP-1 at postnatal weeks 32.6–34.6 and ROP stages were established after birth. BP was measured at the age of 4 years. The ratio (IGF-1)²/IGFBP-1 was created to investigate the influence of both IGF-1 and IGFBP-1 to later BP.

Results

Diastolic BP correlated with IGFBP-1, inversely correlated with IGF-1 and IGF-1²/IGFBP-1 (r = −0.71, p < 0.0001) and positively correlated with catch-up growth velocity from lowest weight SDS to age 36.5 weeks (r = 0.48, p < 0.01), independent of gestational age. Children with moderate-to-severe ROP as neonates had higher mean arterial BP [78 (±95%CI 74–83) vs 71 (±95%CI 68–75) mm Hg, p < 0.05] adjusted for gestational age and birthweight SDS compared to children diagnosed with no to mild ROP.

Conclusion

Low neonatal IGF-1²/IGFBP-1 and severe ROP were associated with higher BP in 4-year-old children born very preterm and may thus predict future cardiovascular morbidity.

Transcriptional responses to temperature and low oxygen stress in Atlantic salmon studied with next-generation sequencing technology

Background

Warmer seawater as a result of climate change may impose environmental challenges for Atlantic salmon aquaculture in its southernmost geographic range. Seawater temperatures above optimal level for growth may be reached in the warmest summer weeks. Caged fish can experience temperature and low oxygen saturation stress during such episodes, raising fish welfare and productivity concerns. In this work we compare the transcriptional responses in Atlantic salmon exposed to chronic high temperature (19°C) and low oxygen saturation (4-5 mg/L) stress.

Results

We used next-generation sequencing and RT-qPCR to screen for effects, and focused on growth regulation and oxidative stress in fish exposed to sub-optimal conditions. Both prolonged temperature (45 days) and low oxygen (120 days) stress had a significant negative effect on growth. The main effect of heat stress appears to be a general reduced transcriptional rate in salmon liver, while mechanisms typically associated with responses induced by chemical drugs were stimulated. Heat stress significantly down-regulated several transcripts encoding proteins involved in the protection against oxidative stress, including CuZn SOD, Mn SOD, GPx1 and GR, as well as additional stress markers HIF1A, CYP1A, MTOR and PSMC2 (RT-qPCR data). In salmon held at low oxygen concentration for four months protein ubiquitination (protein catabolism) was the most strongly affected pathway. According to the RT-qPCR data, low oxygen stress significantly up-regulated the transcriptional levels of IGFBP1B and down-regulated the levels of GR. Pathway analysis suggests that high temperature and low oxygen saturation stress affects many similar mechanisms in Atlantic salmon. Based on the gene lists, six out of the top ten predicted upstream transcriptional regulators, 1,2-dithiol-3-thione sirolimus, CD437, 5-fluorouracil, HNF4A and NFE2L2, were similar between the two treatments.

Conclusions

In conclusion, temperature and low oxygen saturation stress affect many identical mechanisms in liver cells resulting in a metabolic depression, but these effects are not necessarily mediated through altered transcription of the same genes.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-14-817) contains supplementary material, which is available to authorized users.

Regulation of skeletal muscle growth in fish by the growth hormone--insulin-like growth factor system

The growth hormone (GH)-insulin-like growth factor (IGF) system is the key promoter of growth in vertebrates; however, how this system modulates muscle mass in fish is just recently becoming elucidated. In fish, the GH induces muscle growth by modulating the expression of several genes belonging to the myostatin (MSTN), atrophy, GH, and IGF systems as well as myogenic regulatory factors (MRFs). The GH controls the expression of igf1 via Janus kinase 2 (JAK2)/signal transducers and activators of the transcription 5 (STAT5) signaling pathway, but it seems that it is not the major regulator. These mild effects of the GH on igf1 expression in fish muscle seem to be related with the presence of higher contents of truncated GH receptor1 (tGHR1) than full length GHR (flGHR1). IGFs in fish stimulate myogenic cell proliferation, differentiation, and protein synthesis through the MAPK/ERK and PI3K/AKT/TOR signaling pathways, concomitant with abolishing protein degradation and atrophy via the PI3K/AKT/FOXO signaling pathway. Besides these signaling pathways control the expression of several genes belonging to the atrophy and IGF systems. Particularly, IGFs and amino acid control the expression of igf1, thus, suggesting other of alternative signaling pathways regulating the transcription of this growth factor. The possible role of IGF binding proteins (IGFBPs) and the contribution of muscle-derived versus hepatic-produced IGF1 on fish muscle growth is also addressed. Thus, a comprehensive overview on the GH-IGF system regulating fish skeletal muscle growth is presented, as well as perspectives for future research in this field.

Identification of HIF-1α promoter and expression regulation of HIF-1α gene by LPS and hypoxia in zebrafish

The ubiquitously expressed hypoxia-inducible factor-1α (HIF-1α) acts as a key transcription factor in regulating metabolism, development, cellular survival, proliferation and pathology under hypoxia condition. Compared to mammals, fish are more vulnerable to hypoxia stress and contamination; however, the regulation of HIF-1α in fish remains obscure. In this study, zebrafish HIF-1α promoter was cloned and found to possess a CpG island located at -97 to +403, but the canonical TATA-box was absent. Aligning 240-bp HIF-1α proximal promoter region of zebrafish with other vertebrates showed more than 82 % identity with cyprinid fishes. Further luciferase analysis suggested that the minimal core promoter might locate at -134 to +97, and several putative transcription factor binding sites were found in this region by bioinformatic analysis. Moreover, it was shown that the zebrafish HIF-1α mRNA was significantly activated by 10 μg/mL lipopolysaccharide (LPS) under hypoxia condition and peaked at 8 h after treatment, suggesting LPS- and hypoxia-regulated zebrafish HIF-1α transcriptional activity in a synergistic pattern. This synergistic effect was closely related to the living environment of fish, indicating that this mechanism would be more conducive to fish survival.

Toxicogenomic responses of zebrafish embryos/larvae to tris(1,3-dichloro-2-propyl) phosphate (TDCPP) reveal possible molecular mechanisms of developmental toxicity

Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is frequently present in indoor dust and can be detected in human milk. In order to evaluate the effects of TDCPP on vertebrate development, zebrafish embryos/larvae were used as an animal model to examine developmental phenotypes and explore possible mechanisms of toxicity by employing microarrays and iTRAQ labeling quantitative proteomics. The results demonstrated that treatment with TDCPP (3 μM) from 0.75 h postfertilization (hpf) inhibited cell rearrangement at 4 hpf, caused delay in epiboly at 5.7 and 8.5 hpf, and led to abnormal development (e.g., short tail, reduced body size) and lethality between 14 and 45 hpf, which might be related with altered expression of genes regulating embryogenesis. Furthermore, trunk curvature was observed as the main phenotype in 96 hpf zebrafish larvae exposed to 1 or 3 μM TDCPP, possibly by changing somite formation and expression of proteins related to fast muscle and cartilage development. Collectively, our results suggest that exposure to TDCPP causes developmental toxicity in vertebrates and warrant the need for studies to evaluate the potential health risks of TDCPP to developing human embryos/infants/children, due to its frequent presence in indoor dust and potential for human exposure.

Distinct post-transcriptional regulation of Igfbp1 gene by hypoxia in lowland mouse and Qinghai-Tibet plateau root vole Microtus oeconomus

Our previous study revealed the particular expression patterns of insulin-like growth factor 1 (IGF1) and insulin-like growth factor binding protein 1 (IGFBP1) in the Qinghai-Tibet plateau root vole (Microtus oeconomus) under hypoxic challenge. Here we report the molecular mechanisms of Igf gene regulation associated with adaptation to hypoxia. M. oeconomus IGF1 and IGFBP1 were shown to be highly conserved. Hypoxia (8.0% O2, 6h) did not change the liver-derived Igf1 expression in either M. oeconomus or mouse. Hypoxia significantly upregulated hepatic Igfbp1 gene expression and IGFBP1 levels in the liver and plasma of the mouse, but not in M. oeconomus. A functional U-rich element in the 3' untranslated region was found in mouse Igfbp1 mRNA, which was associated with Igfbp1 mRNA stabilization and upregulation under hypoxia, and this U-rich element was eliminated in the M. oeconomus Igfbp1, resulting in blunted Igfbp1 mRNA upregulation, which might be understood as a sequence variation modified during molecular evolution under hypoxia.

Chronic hypoxia exposure of trout embryos alters swimming performance and cardiac gene expression in larvae

Hypoxia exposure during embryonic development of rainbow trout causes developmental delay and bradycardia and alters the ontogeny of cardiac regulatory control mechanisms. The purpose of this study was to characterize how hypoxia exposure from the day of fertilization until stage 34 (57 d postfertilization) affects the aerobic fitness and growth of the hatched fish at multiple stages. In addition, we characterized the expression of gene transcripts for seven troponin I (TnI) isoforms to examine the effect of hypoxia treatment on cardiac muscle development. Results demonstrate that the critical swimming speed of the hypoxia-exposed fish was significantly less than that of the control group at stage 35 and the fry stage. Growth was reduced in the hypoxia-treated fish between stages 35 and 37, as was the relative lipid content at stage 37. Finally, six TnI isoforms were found in all hearts. One of these isoforms, RTcTnI, decreased in abundance between stage 35 and the fry stage, but hypoxia-exposed fish had higher levels than did controls at the fry stage. The abundance of AScTnI2 was significantly lower in hypoxia-exposed fry fish than in controls. These results indicate that chronic hypoxia exposure during embryonic development has long-term consequences on aerobic fitness, growth, and cardiac gene expression following hatch.

Strategies for hypoxia adaptation in fish species: a review

Aquatic environments exhibit wide temporal and spatial variations in oxygen levels compared to terrestrial environments. Fish are an excellent model for elucidating the underlying mechanisms of hypoxia adaptation. Over the past decade, several hypoxia-related proteins have been reported to act in concert to convey oxygen change information to downstream signaling effectors. Some signaling pathways, such as redox status, AMPK, MAPK and IGF/PI3K/Akt, are known to play a central role in hypoxia adaptation. These networks regulate oxygen-sensitive transcription factors which, in turn, affect the expression of hypoxia adaptation-related genes. This review summarizes current insights into hypoxia adaptation-related proteins and signaling pathways in fish.

Hormonal and nutritional drivers of intrauterine growth

PURPOSE OF REVIEW

Size at birth is critical in determining life expectancy with both small and large neonates at risk of shortened life spans. This review examines the hormonal and nutritional drivers of intrauterine growth with emphasis on the role of foetal hormones as nutritional signals in utero.

RECENT FINDINGS

Nutrients drive intrauterine growth by providing substrate for tissue accretion, whereas hormones regulate nutrient distribution between foetal oxidative metabolism and mass accumulation. The main hormonal drivers of intrauterine growth are insulin, insulin-like growth factors and thyroid hormones. Together with leptin and cortisol, these hormones control cellular nutrient uptake and the balance between accretion and differentiation in regulating tissue growth. They also act indirectly via the placenta to alter the materno-foetal supply of nutrients and oxygen. By responding to nutrient and oxygen availability, foetal hormones optimize the survival and growth of the foetus with respect to its genetic potential, particularly during adverse conditions. However, changes in the intrauterine growth of individual tissues may alter their function permanently.

SUMMARY

In both normal and compromised pregnancies, intrauterine growth is determined by multiple hormonal and nutritional drivers which interact to produce a specific pattern of intrauterine development with potential lifelong consequences for health.

Plasticity of cardiovascular function in snapping turtle embryos (Chelydra serpentina): chronic hypoxia alters autonomic regulation and gene expression

Reptile embryos tolerate large decreases in the concentration of ambient oxygen. However, we do not fully understand the mechanisms that underlie embryonic cardiovascular short- or long-term responses to hypoxia in most species. We therefore measured cardiac growth and function in snapping turtle embryos incubated under normoxic (N21; 21% O₂) or chronic hypoxic conditions (H10; 10% O₂). We determined heart rate (fH) and mean arterial pressure (Pm) in acute normoxic (21% O₂) and acute hypoxic (10% O₂) conditions, as well as embryonic responses to cholinergic, adrenergic, and ganglionic pharmacological blockade. Compared with N21 embryos, chronic H10 embryos had smaller bodies and relatively larger hearts and were hypotensive, tachycardic, and following autonomic neural blockade showed reduced intrinsic fH at 90% of incubation. Unlike other reptile embryos, cholinergic and ganglionic receptor blockade both increased fH. β-Adrenergic receptor blockade with propranolol decreased fH, and α-adrenergic blockade with phentolamine decreased Pm. We also measured cardiac mRNA expression. Cholinergic tone was reduced in H10 embryos, but cholinergic receptor (Chrm2) mRNA levels were unchanged. However, expression of adrenergic receptor mRNA (Adrb1, Adra1a, Adra2c) and growth factor mRNA (Igf1, Igf2, Igf2r, Pdgfb) was lowered in H10 embryos. Hypoxia altered the balance between cholinergic receptors, α-adrenoreceptor and β-adrenoreceptor function, which was reflected in altered intrinsic fH and adrenergic receptor mRNA levels. This is the first study to link gene expression with morphological and cardioregulatory plasticity in a developing reptile embryo.

Pregnancy-associated plasma protein A (PAPP-A) modulates the early developmental rate in zebrafish independently of its proteolytic activity

Pregnancy-associated plasma protein-A (PAPP-A) is a large metalloproteinase specifically cleaving insulin-like growth factor (IGF) binding proteins, causing increased IGF bioavailability and, hence, local regulation of IGF receptor activation. We have identified two highly conserved zebrafish homologs of the human PAPP-A gene. Expression of zebrafish Papp-a, one of the two paralogs, begins during gastrulation and persists throughout the first week of development, and analyses demonstrate highly conserved patterns of expression between adult zebrafish, humans, and mice. We show that the specific knockdown of zebrafish papp-a limits the developmental rate beginning during gastrulation without affecting the normal patterning of the embryo. This phenotype is different from those resulting from deficiency of Igf receptor or ligand in zebrafish, suggesting a function of Papp-a outside of the Igf system. Biochemical analysis of recombinant zebrafish Papp-a demonstrates conservation of proteolytic activity, specificity, and the intrinsic regulatory mechanism. However, in vitro transcribed mRNA, which encodes a proteolytically inactive Papp-a mutant, recues the papp-a knockdown phenotype as efficiently as wild-type Papp-a. Thus, the developmental phenotype of papp-a knockdown is not a consequence of lacking Papp-a proteolytic activity. We conclude that Papp-a possesses biological functions independent of its proteolytic activity. Our data represent the first evidence for a non-proteolytic function of PAPP-A.

Experimental pain and opioid analgesia in volunteers at high risk for obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is characterized by recurrent nocturnal hypoxia and sleep disruption. Sleep fragmentation caused hyperalgesia in volunteers, while nocturnal hypoxemia enhanced morphine analgesic potency in children with OSA. This evidence directly relates to surgical OSA patients who are at risk for airway compromise due to postoperative use of opioids. Using accepted experimental pain models, we characterized pain processing and opioid analgesia in male volunteers recruited based on their risk for OSA.

Methods

After approval from the Intitutional Review Board and informed consent, we assessed heat and cold pain thresholds and tolerances in volunteers after overnight polysomnography (PSG). Three pro-inflammatory and 3 hypoxia markers were determined in the serum. Pain tests were performed at baseline, placebo, and two effect site concentrations of remifentanil (1 and 2 µg/ml), an μ-opioid agonist. Linear mixed effects regression models were employed to evaluate the association of 3 PSG descriptors [wake after sleep onset, number of sleep stage shifts, and lowest oxyhemoglobin saturation (SaO₂) during sleep] and all serum markers with pain thresholds and tolerances at baseline, as well as their changes under remifentanil.

Results

Forty-three volunteers (12 normal and 31 with a PSG-based diagnosis of OSA) were included in the analysis. The lower nadir SaO₂ and higher insulin growth factor binding protein-1 (IGFBP-1) were associated with higher analgesic sensitivity to remifentanil (SaO₂, P = 0.0440; IGFBP-1, P = 0.0013). Other pro-inflammatory mediators like interleukin-1β and tumor necrosis factor-α (TNF-α) were associated with an enhanced sensitivity to the opioid analgesic effect (IL-1β, P = 0.0218; TNF-α, P = 0.0276).

Conclusions

Nocturnal hypoxemia in subjects at high risk for OSA was associated with an increased potency of opioid analgesia. A serum hypoxia marker (IGFBP-1) was associated with hypoalgesia and increased potency to opioid analgesia; other pro-inflammatory mediators also predicted an enhanced opioid potency.

Trial Registration: ClinicalTrials.gov

NCT00672737.

Evolution of ancient functions in the vertebrate insulin-like growth factor system uncovered by study of duplicated salmonid fish genomes

Whole-genome duplication (WGD) was experienced twice by the vertebrate ancestor (2 rounds; 2R), again by the teleost fish ancestor (3R) and most recently in certain teleost lineages (4R). Consequently, vertebrate gene families are often expanded in 3R and 4R genomes. Arguably, many types of “functional divergence” present across 2R gene families will exceed that between 3R/4R paralogs of genes comprising 2R families. Accordingly, 4R offers a form of replication of 2R. Examining whether this concept has implications for molecular evolutionary research, we studied insulin-like growth factor (IGF) binding proteins (IGFBPs), whose six 2R family members carry IGF hormones and regulate interactions between IGFs and IGF1-receptors (IGF1Rs). Using phylogenomic approaches, we resolved the complete IGFBP repertoire of 4R-derived salmonid fishes (19 genes; 13 more than human) and established evolutionary relationships/nomenclature with respect to WGDs. Traits central to IGFBP action were determined for all genes, including atomic interactions in IGFBP–IGF1/IGF2 complexes regulating IGF–IGF1R binding. Using statistical methods, we demonstrate that attributes of these protein interfaces are overwhelming a product of 2R IGFBP family membership, explain 49–68% of variation in IGFBP mRNA concentration in several different tissues, and strongly predict the strength and direction of IGFBP transcriptional regulation under differing nutritional states. The results support a model where vertebrate IGFBP family members evolved divergent structural attributes to provide distinct competition for IGFs with IGF1Rs, predisposing different functions in the regulation of IGF signaling. Evolution of gene expression then acted to ensure the appropriate physiological production of IGFBPs according to their structural specializations, leading to optimal IGF-signaling according to nutritional-status and the endocrine/local mode of action. This study demonstrates that relatively recent gene family expansion can facilitate inference of functional evolution within ancient genetic systems.

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

Expression profiling and gene ontology analysis in fathead minnow (Pimephales promelas) liver following exposure to pulp and paper mill effluents

Many studies link pulp and paper mill effluent (PPME) exposure to adverse effects in fish populations present in the mill receiving environments. These impacts are often characteristic of endocrine disruption and may include impaired reproduction, development and survival. While these physiological endpoints are well-characterized, the molecular mechanisms causing them are not yet understood. To investigate changes in gene transcription induced by exposure to a PPME at several stages of treatment, male and female fathead minnows (FHMs) were exposed for 6 days to 25% (v/v) secondary (biologically) treated kraft effluent (TK) or 100% (v/v) combined mill outfall (CMO) from a mill producing both kraft pulp and newsprint. The gene expression changes in the livers of these fish were analyzed using a 22K oligonucleotide microarray. Exposure to TK or CMO resulted in significant changes in the expression levels of 105 and 238 targets in male FHMs and 296 and 133 targets in females, respectively. Targets were then functionally analyzed using gene ontology tools to identify the biological processes in fish hepatocytes that were affected by exposure to PPME after its secondary treatment. Proteolysis was affected in female FHMs exposed to both TK and CMO. In male FHMs, no processes were affected by TK exposure, while sterol, isoprenoid, steroid and cholesterol biosynthesis and electron transport were up-regulated by CMO exposure. The results presented in this study indicate that short-term exposure to PPMEs affects the expression of reproduction-related genes in the livers of both male and female FHMs, and that secondary treatment of PPMEs may not neutralize all of their metabolic effects in fish. Gene ontology analysis of microarray data may enable identification of biological processes altered by toxicant exposure and thus provide an additional tool for monitoring the impact of PPMEs on fish populations.

Molecular, functional, and gene expression analysis of zebrafish hypoxia-inducible factor-3α

Hypoxia-inducible factors 1-3 (HIF1-3) are transcription factors that regulate gene expression in response to hypoxia. Compared with our extensive understanding of HIF-1 and HIF-2, our knowledge of HIF-3 is limited. In this study, we characterized the zebrafish hif-3α gene and determined its temporal and spatial expression, physiological regulation, and biological activity. We show that the chromosomal location, gene structure, and protein structure of zebrafish hif-3α are similar to its mammalian orthologs. When tagged with enhanced green fluorescent protein and transfected into cultured cells, zebrafish Hif-3α was localized in the nucleus and stimulated reporter gene expression in a hypoxia response element-dependent manner. During early development, hif-3α mRNA was detected in all tissues with higher levels in the head. This expression pattern became more apparent in larvae at the 72, 96, and 120 hours post fertilization stages. In the adult stage, hif-3α mRNA was detected in all examined tissues with the highest levels in the ovary. Hypoxia treatment increased Hif-3α protein levels in both embryos and adults. Hypoxia also increased hif-3α mRNA expression levels, and this regulation was tissue-specific. Expression of a stabilized form of Hif-1α in zebrafish embryos increased the expression of igfbp-1a, a Hif-1 target gene, whereas it did not change hif-3α mRNA levels, suggesting that hif-3α is not a Hif-1α target. These results provide new information about the structural and functional conservation, spatial and temporal expression, and physiological regulation of hif-3α in a teleost model organism.

Experimental selection for body size at age modifies early life-history traits and muscle gene expression in adult zebrafish

The short generation time of the zebrafish (Danio rerio) was exploited to investigate the effects of selection for body size at age on early life-history traits and on the transcriptional response to a growth stimulus in skeletal muscle of adult fish. Replicate populations were either unselected (U-lineage) or subjected to four generations of experimental selection for small (S-lineage) or large (L-lineage) body size at 90 days post-fertilization. Body mass was on average 16.3% and 41.0% higher in the L- than in the U- and S-lineages, respectively. Egg diameter was 6.4% lower with 13% less yolk in the S-lineage compared with the other lineages. Maternal transcripts for igf2r, bmpr1aa, igf1ar, igf2a, igfbp5a, ghra and igfbp3 in 2-4 cell stage embryos were higher in the L- than in the S-lineage. Larvae from the L-lineage were significantly larger, but survivorship at the end of the first month was similar between lineages. Gene expression was measured in the fast muscle of adult fish fasted for 7 days and then re-fed to satiation for 48 h. The expression of 11 insulin-like growth factor pathway genes and 12 other nutritionally responsive genes was similar for the S- and L-lineages as was gut fullness with feeding. Transcript abundance for four genes (igf1a, igf2r, igfbp1a and igfbp1b) showed either regulated or constitutive differences between the S- and L-lineages. For example, igf2 receptor transcript abundance was higher and igbp1a/b transcript abundance was lower in the L- than in the S-lineage, consistent with an effect of selection on insulin-like growth factor signalling.

Dynamic transcriptional regulation of autocrine/paracrine igfbp1, 2, 3, 4, 5, and 6 in the skeletal muscle of the fine flounder during different nutritional statuses

The IGF-binding proteins (IGFBPs) play a dual role in the regulation of the activity and bioavailability of IGFs in different tissues. Diverse evidence has shown that IGFBPs can inhibit and/or potentiate IGF actions. In this study, igfbp1, 2, 3, 4, 5, and 6 were isolated in the fine flounder, a flat fish species that shows slow growth and inherent Gh resistance in muscle. Subsequently, the expression of all igfbps was assessed in the skeletal muscle of flounder that underwent different nutritional statuses. igfbp1 was not expressed in muscle during any of the nutritional conditions, whereas igfbp3 and igfbp5 were the lowest and the highest igfbps expressed respectively. A dynamic expression pattern was found in all the igfbps expressed in skeletal muscle, which depended on the nutritional status and sampling period. During the fasting period, igfbp2, 4, and 5 were downregulated, whereas igfbp3 was upregulated during part of the fasting period. The restoration of food modulated the expression of the igfbps dynamically, showing significant changes during both the long- and short-term refeeding. igfbp3 and igfbp6 were downregulated during short-term refeeding, whereas igfbp5 was upregulated, and igfbp2 and igfbp4 remained stable. During long-term refeeding, the expression of igfbp2, 4, 5, and 6 increased, while igfbp3 remained unchanged. In conclusion, this study shows for the first time the isolation of all igfbps in a single fish species, in addition to describing a dynamic nutritional and time-dependent response in the expression of igfbps in the skeletal muscle of a nonmammalian species.

Hypoxia disruption of vertebrate CNS pathfinding through ephrinB2 Is rescued by magnesium

The mechanisms of hypoxic injury to the developing human brain are poorly understood, despite being a major cause of chronic neurodevelopmental impairments. Recent work in the invertebrate Caenorhabditis elegans has shown that hypoxia causes discrete axon pathfinding errors in certain interneurons and motorneurons. However, it is unknown whether developmental hypoxia would have similar effects in a vertebrate nervous system. We have found that developmental hypoxic injury disrupts pathfinding of forebrain neurons in zebrafish (Danio rerio), leading to errors in which commissural axons fail to cross the midline. The pathfinding defects result from activation of the hypoxia-inducible transcription factor (hif1) pathway and are mimicked by chemical inducers of the hif1 pathway or by expression of constitutively active hif1α. Further, we found that blocking transcriptional activation by hif1α helped prevent the guidance defects. We identified ephrinB2a as a target of hif1 pathway activation, showed that knock-down of ephrinB2a rescued the guidance errors, and showed that the receptor ephA4a is expressed in a pattern complementary to the misrouting axons. By targeting a constitutively active form of ephrinB2a to specific neurons, we found that ephrinB2a mediates the pathfinding errors via a reverse-signaling mechanism. Finally, magnesium sulfate, used to improve neurodevelopmental outcomes in preterm births, protects against pathfinding errors by preventing upregulation of ephrinB2a. These results demonstrate that evolutionarily conserved genetic pathways regulate connectivity changes in the CNS in response to hypoxia, and they support a potential neuroprotective role for magnesium.

How hypoxia damages the developing human brain is poorly understood, despite being a major cause of life-long neurologic and psychiatric problems. Premature infants are especially at risk for these problems, with increased rates of attention-deficit disorder, autism, cerebral palsy, epilepsy, psychiatric disorders, and cognitive impairment. It is unknown whether hypoxia can cause errors in the connections of neurons in the vertebrate nervous system. We used zebrafish, a vertebrate model animal, to answer this question. We found that hypoxic injury causes errors in how neurons connect. We went on to determine that a specific genetic pathway, the hif1 pathway, is activated by hypoxia and turns on downstream genes, which cause the connection problems. One of the genes activated by hif1, ephrinB2a, is responsible for many of the connection problems. Importantly, magnesium, used as a treatment for some preterm births, is able to help protect against the neuron connection errors. Our results show that hypoxia in vertebrates does cause errors in neuron connections and that magnesium can help prevent this.

Circulating salmon 28- and 22-kDa insulin-like growth factor binding proteins (IGFBPs) are co-orthologs of IGFBP-1

Circulating insulin-like growth factor binding proteins (IGFBPs) play pivotal roles in stabilizing IGFs and regulating their availability to target tissues. In the teleost circulation, three major IGFBPs are typically detected by ligand blotting with molecular masses around 20-25, 28-32 and 40-45kDa. However, their identity is poorly established and often confused. We previously identified salmon 22- and 41-kDa forms as IGFBP-1 and -2b, respectively. In the present study, we cloned the cDNA of 28-kDa IGFBP from Chinook salmon (Oncorhynchus tshawytscha) as well as rainbow trout (Oncorhynchus mykiss) based on the partial N-terminal amino acid sequence of purified protein and identified it as an ortholog of IGFBP-1. Structural and phylogenetic analyses revealed that the 28-kDa IGFBP is more closely related to human IGFBP-1 and zebrafish IGFBP-1a than the previously identified salmon IGFBP-1 (i.e. 22-kDa IGFBP). We thus named salmon 28- and 22-kDa forms as IGFBP-1a and -1b, respectively. Salmon IGFBP-1a contains a potential PEST region involved in rapid protein turnover and phosphorylation sites typically found in mammalian IGFBP-1, although the PEST and phosphorylation scores are not as high as those of human IGFBP-1. There was a striking difference in tissue distribution patterns between subtypes; Salmon igfbp-1a was expressed in a variety of tissues while igfbp-1b was almost exclusively expressed in the liver, suggesting that IGFBP-1a has more local actions. Direct seawater exposure (osmotic stress) of Chinook salmon parr caused increases in both IGFBP-1s in plasma, while IGFBP-1b appeared to be more sensitive. The presence of two co-orthologs of IGFBP-1 in the circulation in salmon, and most likely in other teleosts, provides a good opportunity to investigate subfunction partitioning of duplicated IGFBP-1 during postnatal growth.

Gene expression patterns of insulin-like growth factor 1, insulin-like growth factor 2 and insulin-like growth factor binding protein 3 in human placenta from pregnancies with intrauterine growth restriction

INTRODUCTION

In this study, we compared insulin-like growth factor (IGF)-gene expression patterns and characteristics of glucose and insulin metabolism in human placenta from pregnancies with or without intrauterine growth restriction (IUGR).

MATERIALS AND METHODS

We compared 101 human placentas from intrauterine growth restriction pregnancies to those of 140 normal pregnancies treated at our department in a one-year period. We have also assessed the serum glucose and insulin levels of the IUGR and control groups. Several possible predicting factors of IUGR were also investigated.

RESULTS

Risk for IUGR was suggested by gestational weight gain and gestational increase in maternal body mass index (BMI) as well as maternal birthweight. In pregnancies without IUGR, umbilical cord glucose and insulin levels were significantly higher than in pregnancies with IUGR. In placentas from pregnancies with IUGR an overexpression of the IGF-2 and the insulin-like growth factor binding protein (IGFBP)-3 genes was found. In placentas from pregnancies with male fetal gender we found a significant overexpression of the IGF-2 gene.

DISCUSSION

Gestational weight gain and BMI increase seem to predict the development of IUGR. Insulin and carbohydrate metabolism are also impaired in IUGR fetuses. In the placentas from pregnancies with IUGR, IGF-2 is overexpressed reflecting its physiological role in optimizing energy distribution in a low-energy environment.

The effects of mitochondrial genotype on hypoxic survival and gene expression in a hybrid population of the killifish, Fundulus heteroclitus

The physiological link between oxygen availability and mitochondrial function is well established. However, whether or not fitness variation is associated with mitochondrial genotypes in the field remains a contested topic in evolutionary biology. In this study, we draw on a population of the teleost fish, Fundulus heteroclitus, where functionally distinct subspecies hybridize, likely as a result of past glacial events. We had two specific aims: (i) to determine the effect of mtDNA genotype on survivorship of male and female fish under hypoxic stress and (ii) to determine the effect of hypoxic stress, sex and mtDNA genotype on gene expression. We found an unexpected and highly significant effect of sex on survivorship under hypoxic conditions, but no significant effect of mtDNA genotype. Gene expression analyses revealed hundreds of transcripts differentially regulated by sex and hypoxia. Mitochondrial transcripts and other predicted pathways were among those influenced by hypoxic stress, and a transcript corresponding to the mtDNA control region was the most highly suppressed transcript under the conditions of hypoxia. An RT-PCR experiment on the control region was consistent with microarray results. Effects of mtDNA sequence variation on genome expression were limited; however, a potentially important epistasis between mtDNA sequence and expression of a nuclear-encoded mitochondrial translation protein was discovered. Overall, these results confirm that mitochondrial regulation is a major component of hypoxia tolerance and further suggest that purifying selection has been the predominant selective force on mitochondrial genomes in these two subspecies.

Characterization of three IGFBP mRNAs in Atlantic croaker and their regulation during hypoxic stress: potential mechanisms of their upregulation by hypoxia

Insulin-like growth factor-binding proteins (IGFBPs) play important roles in downregulating IGF activity and growth and development in vertebrates under hypoxic stress. However, the mechanisms of hypoxia regulation of IGFBPs in teleost fishes are unknown. The involvement of reactive oxygen species (ROS) and hypoxia-inducible factors (HIFs) in hypoxia upregulation of IGFBPs in Atlantic croaker were investigated. Three croaker IGFBPs, IGFBP-1, IGFBP-2, and IGFBP-5, were cloned and characterized. Chronic hypoxia exposure [dissolved oxygen (DO): 1.7 mg/l for 2-4 wk] caused significant increases in hepatic and neural IGFBP-1 mRNA expression compared with tissue mRNA levels in fish held under normoxic conditions (6.5 mg DO/l). Moreover, longer-term chronic hypoxia exposure (2-2.7 mg DO/l for 15-20 wk) caused significant increases in mRNA levels of all three IGFBPs in both liver and brain tissues. Hypoxia exposure also markedly increased superoxide radical (O(2)(·-), an index of ROS) production and HIF-1α mRNA and HIF-2α protein expression in croaker livers. Pharmacological treatment with an antioxidant attenuated the hypoxia-induced increases in O(2)(·-) production and HIFα mRNA and protein expression as well as the elevation of IGFBP-1 mRNA levels. These results suggest that the upregulation of IGFBP expression under hypoxia stress is due, in part, to alterations in the antioxidant status, which may involve ROS and HIFs.

Hypoxia impairs primordial germ cell migration in zebrafish (Danio rerio) embryos

BACKGROUND

As a global environmental concern, hypoxia is known to be associated with many biological and physiological impairments in aquatic ecosystems. Previous studies have mainly focused on the effect of hypoxia in adult animals. However, the effect of hypoxia and the underlying mechanism of how hypoxia affects embryonic development of aquatic animals remain unclear.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study, the effect of hypoxia on primordial germ cell (PGC) migration in zebrafish embryos was investigated. Hypoxic embryos showed PGC migration defect as indicated by the presence of mis-migrated ectopic PGCs. Insulin-like growth factor (IGF) signaling is required for embryonic germ line development. Using real-time PCR, we found that the mRNA expression levels of insulin-like growth factor binding protein (IGFBP-1), an inhibitor of IGF bioactivity, were significantly increased in hypoxic embryos. Morpholino knockdown of IGFBP-1 rescued the PGC migration defect phenotype in hypoxic embryos, suggesting the role of IGFBP-1 in inducing PGC mis-migration.

CONCLUSIONS/SIGNIFICANCE

This study provides novel evidence that hypoxia disrupts PGC migration during embryonic development in fish. IGF signaling is shown to be one of the possible mechanisms for the causal link between hypoxia and PGC migration. We propose that hypoxia causes PGC migration defect by inhibiting IGF signaling through the induction of IGFBP-1.

IGF binding protein 1 is correlated with hypoxia-induced growth reduce and developmental defects in grass carp (Ctenopharyngodon idellus) embryos

The effects of hypoxia on embryonic development and the underlying cellular and molecular mechanisms are poorly understood in teleost fish, although the hypoxic effects on embryonic growth and development have been reported in the zebrafish model. Here, we found that hypoxia caused significant developmental delay and growth retardation during grass carp embryogenesis. Placing the embryos in hypoxic conditions at different developmental stages strongly induced the mRNA expression of insulin-like growth factor-binding protein 1 (IGFBP1), an inhibitory protein that binds to IGF and inhibits its subsequent actions in vivo. Further gain-of-function analysis results provided strong evidence to support the hypothesis that IGFBP1 plays an important role in mediating hypoxic-induced growth and developmental defects. Overexpression of IGFBP1 mRNA reduced the growth rate to a degree that was similar to hypoxia. Additionally, overexpression of IGFBP1 caused significant developmental defects in the formation of midline, somite and hindbrain structures during grass carp embryogenesis. Taken together, our studies suggest that IGFBP1 plays a key role in mediating these hypoxia-induced embryonic growth retardation and developmental delay in grass carp.

Sex differences in prenatal epigenetic programming of stress pathways

Maternal stress experience is associated with neurodevelopmental disorders including schizophrenia and autism. Recent studies have examined mechanisms by which changes in the maternal milieu may be transmitted to the developing embryo and potentially translated into programming of the epigenome. Animal models of prenatal stress have identified important sex- and temporal-specific effects on offspring stress responsivity. As dysregulation of stress pathways is a common feature in most neuropsychiatric diseases, molecular and epigenetic analyses at the maternal-embryo interface, especially in the placenta, may provide unique insight into identifying much-needed predictive biomarkers. In addition, as most neurodevelopmental disorders present with a sex bias, examination of sex differences in the inheritance of phenotypic outcomes may pinpoint gene targets and specific windows of vulnerability in neurodevelopment, which have been disrupted. This review discusses the association and possible contributing mechanisms of prenatal stress in programming offspring stress pathway dysregulation and the importance of sex.

The conserved clusterin gene is expressed in the developing choroid plexus under the regulation of notch but not IGF signaling in zebrafish

Recent genome-wide association studies have implicated the clusterin gene in the etiology of Alzheimer's disease. The expression and function of clusterin in the developing brain, however, is poorly understood. In this study, we have characterized the zebrafish clusterin gene and determined its structural conservation, developmental expression, and physiological regulation. The structure of the zebrafish clusterin gene and protein is similar to its human orthologue. Biochemical assays show that zebrafish Clusterin is a secreted protein that cannot bind IGFs. In adult zebrafish, clusterin mRNA is detected in many tissues. In early development, clusterin mRNA becomes detectable at 12 h postfertilization, and its levels gradually increase thereafter. In situ hybridization analysis indicates that clusterin mRNA is specifically expressed in the developing diencephalic and myelencephalic choroid plexus. Among various stresses tested, heat shock, but not hypoxic or ionic stresses, increases the levels of clusterin mRNA. Inhibition of the IGF-I receptor-mediated signaling or overexpression of IGF ligands did not change clusterin mRNA levels. In comparison, inhibition or targeted knockdown of Notch signaling significantly increased clusterin mRNA expression in choroid plexus. These results suggest that clusterin is a marker of choroid plexus in zebrafish, and its expression in the developing choroid plexus is under the regulation of Notch but not IGF signaling.

Sex-specificity in transgenerational epigenetic programming

Prenatal programming of the epigenome is a critical determinant in offspring outcome and stands at the interface between environment and genetics. Maternal experiences such as stress and obesity are associated with a host of neurodevelopmental and metabolic diseases, some of which have been characterized into the second and third generations. The mechanism through which determinants such as maternal diet or stress contribute to disease development likely involves a complex interaction between the maternal environment, placental changes, and epigenetic programming of the embryo. While we have begun to more fully appreciate and explore the epigenome in determination of disease risk, we know little as to the contribution embryo sex makes in epigenetic regulation. This review discusses the importance of sex differences in the transmission and inheritance of traits that are generated in the prenatal environment using models of maternal stress and diet.

Role of IGF signaling in catch-up growth and accelerated temporal development in zebrafish embryos in response to oxygen availability

Animals respond to adverse environments by slowing down or arresting growth and development. Upon returning to normal conditions, they often show compensatory acceleration in growth and developmental rate. This phenomenon, known as `catch-up' growth, is widely documented in the animal kingdom. The underlying molecular mechanisms, however, are poorly understood. Using the zebrafish embryo as an experimental model system, we tested the hypothesis that changes in IGF signaling activities play an important role in the accelerated growth and temporal development resulting from re-oxygenation following hypoxia. We show that chronic hypoxia reduced, and re-oxygenation accelerated, embryonic growth and developmental rate. Whereas hypoxia repressed the Igf1 receptor and its downstream Erk1/2 and Akt signaling activities, re-oxygenation restored their activities. Specific inhibition of Igf1 receptor signaling during re-oxygenation by genetic and pharmacological approaches attenuated catch-up growth. Further analysis showed that whereas PI3K-Akt is required in both normal and catch-up growth, Mek1/2-Erk1/2 activation induced by elevated IGF signaling during re-oxygenation is particularly crucial for catch-up growth. These results suggest that the evolutionarily conserved IGF signaling pathway coordinates growth and temporal development in zebrafish embryos in response to oxygen availability.

Ontogeny of the corticotropin-releasing factor system in rainbow trout and differential effects of hypoxia on the endocrine and cellular stress responses during development

To further our understanding of the development of the stress axis and the responsiveness of embryonic and larval fish to environmental stressors, this study examined the ontogeny of whole-body cortisol levels and of the corticotropin-releasing factor (CRF) system in rainbow trout, as well as the endocrine and cellular stress responses to hypoxia. After depletion of a maternal deposit, de novo synthesis of cortisol increased exponentially between the 'eyed' stage and first feeding. Whole body CRF mRNA levels dominated over those of the related peptide urotensin I (UI) from hatch through complete yolk sac absorption. The mRNA levels of CRF-binding protein (CRF-BP) closely paralleled those of CRF and UI throughout ontogeny except at first feeding when an increase in CRF gene expression was not matched by change in CRF-BP transcript abundance. In the hypoxia challenge, fish were exposed to 15% O(2) saturation for either 90 min or 24h at three key developmental stages: hatch, swim up and first feeding. While the embryos were unaffected, chronic hypoxia elicited a transient 2-fold increase in whole-body cortisol levels in the larval stages. The hypoxia challenge also generally suppressed the mRNA levels of CRF and CRF-BP, had no effect on the expression of UI, but had a marked stimulatory effect on heat shock protein 70 (Hsp70) gene expression. Taken together, these results suggest a role for the CRF system in the ontogenic regulation of corticosteroidogenesis and show that hypoxia has developmental stage-specific effects on the endocrine and cellular stress responses in rainbow trout.

HIF-1alpha and -2alpha genes in a hypoxia-sensitive teleost species Megalobrama amblycephala: cDNA cloning, expression and different responses to hypoxia

Transcriptional responses to hypoxia are primarily mediated by hypoxia-inducible factor (HIF) alpha subunits, i.e. HIF-1alpha, -2alpha and -3alpha. In fish, the molecular constructions, expression characteristics and hypoxic regulation of HIF-alpha subunits are still not well known. In this study, we identified the HIF-1alpha and HIF-2alpha full-length cDNAs in a hypoxia-sensitive fish species Wuchang bream, Megalobrama amblycephala. The whole length of HIF-1alpha cDNA was 3,815bp, consisting of an open reading frame (ORF) encoding 774 amino acid (aa) residues. The HIF-2alpha cDNA totaled 3,121-bp including an 835-aa ORF. The Wuchang bream HIF-1alpha and HIF-2alpha subunits were structurally similar in the DNA-binding and dimerization domains, but differed in the transactivation domain. In adult fish, both HIF-1alpha and HIF-2alpha mRNAs were detected in different tissues under normoxic conditions. HIF-1alpha mRNA was highly expressed in the liver, gill and testis, whereas HIF-2alpha mRNA was abundantly expressed in most of the Wuchang bream tissues. Both HIF-1alpha and HIF-2alpha mRNAs were detected in all stages of embryogenesis and expressed in a ubiquitous pattern. In contrast to HIF-1alpha, the mRNA levels of HIF-2alpha fluctuated in different stages, with higher expression in the zygote, 8-, 28-, 48- and 52-hr post fertilization (hpf) embryos. During hypoxic treatment, the mRNA levels of HIF-2alpha were significantly (p<0.01) up-regulated to 910% in the liver and 320% in the kidney, whereas no significant changes of HIF-1alpha mRNA were observed in the corresponding tissues. These results suggest that the Wuchang bream HIF-1alpha and -2alpha would be involved in different physiological functions under normoxia and hypoxia situations.

Insulin-like growth factors (IGFs), IGF receptors, and IGF-binding proteins: roles in skeletal muscle growth and differentiation

The insulin-like growth factor (IGF) signaling pathway consists of multiple IGF ligands, IGF receptors, and IGF-binding proteins (IGFBPs). Studies in a variety of animal and cellular systems suggest that the IGF signaling pathway plays a key role in regulating skeletal muscle growth, differentiation, and in maintaining homeostasis of the adult muscle tissues. Intriguingly, IGFs stimulate both myoblast proliferation and differentiation, which are two mutually exclusive biological events during myogenesis. Both of these actions are mediated through the same IGF-1 receptor. Recent studies have shed new insights into the molecular mechanisms underlying these paradoxical actions of IGFs in muscle cells. In this article, we provide a brief review of our current understanding of the IGF signaling system and discuss recent findings on how local oxygen availability and IGFBPs act to specify IGF actions in muscle cells.

Hypoxia converts the myogenic action of insulin-like growth factors into mitogenic action by differentially regulating multiple signaling pathways

Insulin-like growth factors (IGFs) stimulate myoblast proliferation and differentiation. It remains elusive how these mutually exclusive cellular responses are elicited by the same growth factor. Here we report that whereas IGF promotes myoblast differentiation under normoxia, it stimulates proliferation under hypoxia. Hypoxia activates the HIF-1 transcriptional program and knockdown of HIF-1alpha changes the mitogenic action of IGF into myogenic action under hypoxia. Conversely, overexpression of HIF-1alpha abolishes the myogenic effect of IGF under normoxia. Under normoxia, IGF activates the Akt-mTOR, p38, and Erk1/2 MAPK pathways. Hypoxia suppresses basal and IGF-induced Akt-mTOR and p38 activity, whereas it enhances and prolongs IGF-induced Erk1/2 activation in a HIF-1-dependent fashion. Activation of Akt-mTOR and p38 promotes myogenesis, and p38 also inhibits proliferation. Activation of Erk stimulates myoblast proliferation but inhibits differentiation. These results suggest that hypoxia converts the myogenic action of IGFs into mitogenic action by differentially regulating multiple signaling pathways via HIF-1-dependent mechanisms. Our findings provide a mechanistic explanation for the paradoxical actions of IGFs during myogenesis and reveal a novel mechanism by which cells sense and integrate growth factor signals and oxygen availability in their microenvironments.