Selection and analysis of a mutant cell line defective in the hypoxia-inducible factor-1 alpha-subunit (HIF-1alpha). Characterization of hif-1alpha-dependent and -independent hypoxia-inducible gene expression

Extrahepatic Bile Duct Organoids as a Model to Study Ischemia/Reperfusion Injury During Liver Transplantation

Biliary complications are still a major cause for morbidity and mortality after liver transplantation (LT). Ischemia/reperfusion injury (IRI) leads to disruption of the biliary epithelium. We introduce a novel model to study the effect of IRI on human cholangiocytes using extrahepatic cholangiocyte organoids (ECOs). Extrahepatic bile duct tissue was collected during LT at static cold storage and after reperfusion (n = 15); gallbladder tissue was used for controls (n = 5). ECOs (n = 9) were cultured from extrahepatic biliary tissue, with IRI induced in an atmosphere of 95% air (nitrogen), 1% O2 and 5% CO2for 48 h, followed by 24 h of reoxygenation. Qualitative and quantitative histology and qRT-PCR were performed to discern phenotype, markers of hypoxia, programmed cell death and proliferation. ECOs self-organized into circular structures resembling biliary architecture containing cholangiocytes that expressed EpCAM, CK19, LGR5 and SOX-9. After hypoxia, ECOs showed increased expression of VEGF A (p < 0.0001), SLC2A1 (p < 0.0001) and ACSL4 (p < 0.0001) to indicate response to hypoxic damage and subsequent programmed cell death. Increase in cyclin D1 (p < 0.0001) after reoxygenation indicated proliferative activity in ECOs. Therefore, ECO structure and response to IRI are comparable to that found in-vivo, providing a suitable model to study IRI of the bile duct in-vitro.

Cardiac Metabolism

The heart is composed of a heterogeneous mixture of cellular components perfectly intermingled and able to integrate common environmental signals to ensure proper cardiac function and performance. Metabolism defines a cell context-dependent signature that plays a critical role in survival, proliferation, or differentiation, being a recognized master piece of organ biology, modulating homeostasis, disease progression, and adaptation to tissue damage. The heart is a highly demanding organ, and adult cardiomyocytes require large amount of energy to fulfill adequate contractility. However, functioning under oxidative mitochondrial metabolism is accompanied with a concomitant elevation of harmful reactive oxygen species that indeed contributes to the progression of several cardiovascular pathologies and hampers the regenerative capacity of the mammalian heart. Cardiac metabolism is dynamic along embryonic development and substantially changes as cardiomyocytes mature and differentiate within the first days after birth. During early stages of cardiogenesis, anaerobic glycolysis is the main energetic program, while a progressive switch toward oxidative phosphorylation is a hallmark of myocardium differentiation. In response to cardiac injury, different signaling pathways participate in a metabolic rewiring to reactivate embryonic bioenergetic programs or the utilization of alternative substrates, reflecting the flexibility of heart metabolism and its central role in organ adaptation to external factors. Despite the well-established metabolic pattern of fetal, neonatal, and adult cardiomyocytes, our knowledge about the bioenergetics of other cardiac populations like endothelial cells, cardiac fibroblasts, or immune cells is limited. Considering the close intercellular communication and the influence of nonautonomous cues during heart development and after cardiac damage, it will be fundamental to better understand the metabolic programs in different cardiac cells in order to develop novel interventional opportunities based on metabolic rewiring to prevent heart failure and improve the limited regenerative capacity of the mammalian heart.

Cardiac metabolism in HFpEF: from fuel to signalling

Heart failure (HF) is marked by distinctive changes in myocardial uptake and utilization of energy substrates. Among the different types of HF, HF with preserved ejection fraction (HFpEF) is a highly prevalent, complex, and heterogeneous condition for which metabolic derangements seem to dictate disease progression. Changes in intermediate metabolism in cardiometabolic HFpEF-among the most prevalent forms of HFpEF-have a large impact both on energy provision and on a number of signalling pathways in the heart. This dual, metabolic vs. signalling, role is played in particular by long-chain fatty acids (LCFAs) and short-chain carbon sources [namely, short-chain fatty acids (SCFAs) and ketone bodies (KBs)]. LCFAs are key fuels for the heart, but their excess can be harmful, as in the case of toxic accumulation of lipid by-products (i.e. lipotoxicity). SCFAs and KBs have been proposed as a potential major, alternative source of energy in HFpEF. At the same time, both LCFAs and short-chain carbon sources are substrate for protein post-translational modifications and other forms of direct and indirect signalling of pivotal importance in HFpEF pathogenesis. An in-depth molecular understanding of the biological functions of energy substrates and their signalling role will be instrumental in the development of novel therapeutic approaches to HFpEF. Here, we summarize the current evidence on changes in energy metabolism in HFpEF, discuss the signalling role of intermediate metabolites through, at least in part, their fate as substrates for post-translational modifications, and highlight clinical and translational challenges around metabolic therapy in HFpEF.

Hypoxic Incubation Conditions for Optimized Manufacture of Tenocyte-Based Active Pharmaceutical Ingredients of Homologous Standardized Transplant Products in Tendon Regenerative Medicine

Human fetal progenitor tenocytes (hFPT) produced in defined cell bank systems have recently been characterized and qualified as potential therapeutic cell sources in tendon regenerative medicine. In view of further developing the manufacture processes of such cell-based active pharmaceutical ingredients (API), the effects of hypoxic in vitro culture expansion on key cellular characteristics or process parameters were evaluated. To this end, multiple aspects were comparatively assessed in normoxic incubation (i.e., 5% CO₂ and 21% O₂, standard conditions) or in hypoxic incubation (i.e., 5% CO₂ and 2% O₂, optimized conditions). Experimentally investigated parameters and endpoints included cellular proliferation, cellular morphology and size distribution, cell surface marker panels, cell susceptibility toward adipogenic and osteogenic induction, while relative protein expression levels were analyzed by quantitative mass spectrometry. The results outlined conserved critical cellular characteristics (i.e., cell surface marker panels, cellular phenotype under chemical induction) and modified key cellular parameters (i.e., cell size distribution, endpoint cell yields, matrix protein contents) potentially procuring tangible benefits for next-generation cell manufacturing workflows. Specific proteomic analyses further shed some light on the cellular effects of hypoxia, potentially orienting further hFPT processing for cell-based, cell-free API manufacture. Overall, this study indicated that hypoxic incubation impacts specific hFPT key properties while preserving critical quality attributes (i.e., as compared to normoxic incubation), enabling efficient manufacture of tenocyte-based APIs for homologous standardized transplant products.

Mito-targeted antioxidant prevents cardiovascular remodelling in spontaneously hypertensive rat by modulation of energy metabolism

Hypertension induced left ventricular hypertrophy (LVH) augments the risk of cardiovascular anomalies. Mitochondrial alterations result in oxidative stress, accompanied by decrease in fatty acid oxidation, leading to the activation of the hypertrophic program. Targeted antioxidants are expected to reduce mitochondrial reactive oxygen species more effectively than general antioxidants. This study was designed to assess whether the mito-targeted antioxidant, Mito-Tempol (Mito-TEMP) is more effective than the general oxidant, Tempol (TEMP) in reduction of hypertension and hypertrophy and prevention of shift in cardiac energy metabolism. Spontaneously hypertensive rats were administered either TEMP (20 mg/kg/day) or Mito-TEMP (2 mg/kg/day) intraperitoneally for 30 days. Post treatment, animals were subjected to 2D-echocardiography. Myocardial lysates were subjected to RPLC - LTQ-Orbitrap-MS analysis. Mid-ventricular sections were probed for markers of energy metabolism and fibrosis. The beneficial effect on cardiovascular structure and function was significantly higher for Mito-TEMP. Increase in mitochondrial antioxidants and stimulation of fatty acid metabolism; with significant improvement in cardiovascular function was apparent in spontaneously hypertensive rats (SHR) treated with Mito-TEMP. The study indicates that Mito-TEMP is superior to its non- targeted isoform in preventing hypertension induced LVH, and the beneficial effects on heart are possibly mediated by reversal of metabolic remodelling.

Genetic approaches to understand cellular responses to oxygen availability

Oxygen-sensing mechanisms have evolved to allow organisms to respond and adapt to oxygen availability. In metazoans, oxygen-sensing is predominantly mediated by the hypoxia inducible factors (HIFs). These transcription factors are stabilised when oxygen is limiting, activating genes involved in angiogenesis, cell growth, pH regulation and metabolism to reset cell function and adapt to the cellular environment. However, the recognition that other cellular pathways and enzymes can also respond to changes in oxygen abundance provides further complexity. Dissecting this interplay of oxygen-sensing mechanisms has been a key research goal. Here, we review how genetic approaches have contributed to our knowledge of oxygen-sensing pathways which to date have been predominantly focused on the HIF pathway. We discuss how genetic studies have advanced the field and outline the implications and limitations of such approaches for the development of therapies targeting oxygen-sensing mechanisms in human disease.

HIF-1 regulates energy metabolism of the Tibetan chicken brain during embryo development under hypoxia

The Tibetan chicken (Gallus gallus; TBC) is an indigenous breed found in the Qinghai-Tibet Plateau that are well adapted to a hypoxic environment. The energy metabolism of embryonic brains in TBCs under hypoxia has been little reported. This study investigated changes in energy metabolism of the TBC brain during embryo development under hypoxia. We found that TBCs exhibited a change of glycolysis and the tricarboxylic acid cycle during embryo development under hypoxia. Hypoxia-inducible factor (HIF)-1 was potentially involved in this by directly inducing overexpression of pyruvate dehydrogenase kinase 1 (PDK1) and the glycolytic genes hexokinase 1 (HK1) and lactate dehydrogenase A (LDHA) to increase glycolysis of TBCs to adapt to hypoxia. Although these may not be unique to TBCs, as we had also found similar results in Dwarf Laying Chickens, a lowland chicken breed, TBCs had a stronger regulating ability. In summary, our study revealed that HIF-1 induced energy metabolism changes in the TBC brain via upregulating expressions of PDK1 and other HIF-1 target genes like HK1 and LDHA to increase glycolysis for TBC hypoxic adaptations during embryo development. It indicates the potential application of TBC energy metabolism research for other animals living on the Qinghai-Tibet Plateau.

Hypoxia activated long non-coding RNA HABON regulates the growth and proliferation of hepatocarcinoma cells by binding to and antagonizing HIF-1 alpha

The adaptation of tumour cells to hypoxic microenvironment is one of the most significant characteristics of many malignant tumour diseases including hepatocarcinoma. Recently, long non-coding RNAs (lncRNAs) have been reported to play important roles in the various levels of gene regulation thus functioning in growth and survival of tumour cells. Here, new hypoxia-related lncRNAs in hepatocarcinoma cells were screened and validated by lncRNA chip-array as well as real-time RT-PCR. Among them, a hypoxia-activated lncRNA that we identified and termed Hypoxia-Activated BNIP3 Overlapping Non-coding RNA (HABON), was not only regulated by hypoxic-induced factor-1α (HIF-1α) but its expression increased significantly under hypoxia in tumour cells. We deciphered the biological characteristics of HABON including its cell localization, genomic location, as well as its full-length sequence, and proved HABON could promote growth, proliferation and clone-formation of hepatocarcinoma cells under hypoxia. Then, we revealed that HABON was transcriptionally activated by HIF-1α in hypoxic cells, furthermore, it could interact with HIF-1α and promote its protein degradation, thus affecting transcription of HIF-1α's target genes to exert its effects on cells. Besides, the elevated expression of HABON under hypoxia could promote the transcriptional activation of BNIP3 through HIF-1α, and increasing the expression level of BNIP3. This research provides a novel clue for the adaptive survival and growth mechanism of tumour under hypoxia, and gives a way to reveal the nature of tumour cells' resistance characteristics to harsh microenvironment.

LncRNA HOTAIR regulates glucose transporter Glut1 expression and glucose uptake in macrophages during inflammation

Inflammation plays central roles in the immune response. Inflammatory response normally requires higher energy and therefore is associated with glucose metabolism. Our recent study demonstrates that lncRNA HOTAIR plays key roles in NF-kB activation, cytokine expression, and inflammation. Here, we investigated if HOTAIR plays any role in the regulation of glucose metabolism in immune cells during inflammation. Our results demonstrate that LPS-induced inflammation induces the expression of glucose transporter isoform 1 (Glut1) which controls the glucose uptake in macrophages. LPS-induced Glut1 expression is regulated via NF-kB activation. Importantly, siRNA-mediated knockdown of HOTAIR suppressed the LPS-induced expression of Glut1 suggesting key roles of HOTAIR in LPS-induced Glut1 expression in macrophage. HOTAIR induces NF-kB activation, which in turn increases Glut1 expression in response to LPS. We also found that HOTAIR regulates glucose uptake in macrophages during LPS-induced inflammation and its knockdown decreases LPS-induced increased glucose uptake. HOTAIR also regulates other upstream regulators of glucose metabolism such as PTEN and HIF1α, suggesting its multimodal functions in glucose metabolism. Overall, our study demonstrated that lncRNA HOTAIR plays key roles in LPS-induced Glut1 expression and glucose uptake by activating NF-kB and hence HOTAIR regulates metabolic programming in immune cells potentially to meet the energy needs during the immune response.

Hypoxia-inducible factor 1 alpha limits dendritic cell stimulation of CD8 T cell immunity

Dendritic cells are sentinels of the immune system and represent a key cell in the activation of the adaptive immune response. Hypoxia-inducible factor 1 alpha (HIF-1α)–a crucial oxygen sensor stabilized during hypoxic conditions–has been shown to have both activating and inhibitory effects in immune cells in a context- and cell-dependent manner. Previous studies have demonstrated that in some immune cell types, HIF-1α serves a pro-inflammatory role. Genetic deletion of HIF-1α in macrophages has been reported to reduce their pro-inflammatory function. In contrast, loss of HIF-1α enhanced the pro-inflammatory activity of dendritic cells in a bacterial infection model. In this study, we aimed to further clarify the effects of HIF-1α in dendritic cells. Constitutive expression of HIF-1α resulted in diminished immunostimulatory capacity of dendritic cells in vivo, while conditional deletion of HIF-1α in dendritic cells enhanced their ability to induce a cytotoxic T cell response. HIF-1α-expressing dendritic cells demonstrated increased production of inhibitory mediators including IL-10, iNOS and VEGF, which correlated with their reduced capacity to drive effector CD8⁺ T cell function. Altogether, these data reveal that HIF-1α can promote the anti-inflammatory functions of dendritic cells and provides insight into dysfunctional immune responses in the context of HIF-1α activation.

Fetal cardiomyocyte phenotype, ketone body metabolism, and mitochondrial dysfunction in the pathology of atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia diagnosed in clinical practice. Even though hypertension, congestive heart failure, pulmonary disease, and coronary artery disease are the potential risk factors for AF, the underlying molecular pathology is largely unknown. The reversion of the mature cardiomyocytes to fetal phenotype, impaired ketone body metabolism, mitochondrial dysfunction, and the cellular effect of reactive oxygen species (ROS) are the major underlying biochemical events associated with the molecular pathology of AF. On this background, the present manuscript sheds light into these biochemical events in regard to the metabolic derangements in cardiomyocyte leading to AF, especially with respect to structural, contractile, and electrophysiological properties. In addition, the article critically reviews the current understanding, potential demerits, and translational strategies in the management of AF.

Cardiac foetal reprogramming: a tool to exploit novel treatment targets for the failing heart

As the heart matures during embryogenesis from its foetal stages, several structural and functional modifications take place to form the adult heart. This process of maturation is in large part due to an increased volume and work load of the heart to maintain proper circulation throughout the growing body. In recent years, it has been observed that these changes are reversed to some extent as a result of cardiac disease. The process by which this occurs has been characterized as cardiac foetal reprogramming and is defined as the suppression of adult and re-activation of a foetal genes profile in the diseased myocardium. The reasons as to why this process occurs in the diseased myocardium are unknown; however, it has been suggested to be an adaptive process to counteract deleterious events taking place during cardiac remodelling. Although still in its infancy, several studies have demonstrated that targeting foetal reprogramming in heart failure can lead to substantial improvement in cardiac functionality. This is highlighted by a recent study which found that by modulating the expression of 5-oxoprolinase (OPLAH, a novel cardiac foetal gene), cardiac function can be significantly improved in mice exposed to cardiac injury. Additionally, the utilization of angiotensin receptor neprilysin inhibitors (ARNI) has demonstrated clear benefits, providing important clinical proof that drugs that increase natriuretic peptide levels (part of the foetal gene programme) indeed improve heart failure outcomes. In this review, we will highlight the most important aspects of cardiac foetal reprogramming and will discuss whether this process is a cause or consequence of heart failure. Based on this, we will also explain how a deeper understanding of this process may result in the development of novel therapeutic strategies in heart failure.

Exploring the molecular interface between hypoxia-inducible factor signalling and mitochondria

Oxygen is required for the survival of the majority of eukaryotic organisms, as it is important for many cellular processes. Eukaryotic cells utilize oxygen for the production of biochemical energy in the form of adenosine triphosphate (ATP) generated from the catabolism of carbon-rich fuels such as glucose, lipids and glutamine. The intracellular sites of oxygen consumption-coupled ATP production are the mitochondria, double-membraned organelles that provide a dynamic and multifaceted role in cell signalling and metabolism. Highly evolutionarily conserved molecular mechanisms exist to sense and respond to changes in cellular oxygen levels. The primary transcriptional regulators of the response to decreased oxygen levels (hypoxia) are the hypoxia-inducible factors (HIFs), which play important roles in both physiological and pathophysiological contexts. In this review we explore the relationship between HIF-regulated signalling pathways and the mitochondria, including the regulation of mitochondrial metabolism, biogenesis and distribution.

Adenylate kinase 4 modulates oxidative stress and stabilizes HIF-1α to drive lung adenocarcinoma metastasis

Background

Adenylate kinase 4 (AK4) has been identified as a biomarker of metastasis in lung cancer. However, the impacts of AK4 on metabolic genes and its translational value for drug repositioning remain unclear.

Methods

Ingenuity upstream analyses were used to identify potential transcription factors that regulate the AK4 metabolic gene signature. The expression of AK4 and its upstream regulators in lung cancer patients was examined via immunohistochemistry. Pharmacological and gene knockdown/overexpression approaches were used to investigate the interplay between AK4 and its upstream regulators during epithelial-to-mesenchymal transition (EMT). Drug candidates that reversed AK4-induced gene expression were identified by querying a connectivity map. Orthotopic xenograft mouse models were established to evaluate the therapeutic efficacy of drug candidates for metastatic lung cancer.

Results

We found that HIF-1α is activated in the AK4 metabolic gene signature. IHC analysis confirmed this positive correlation, and the combination of both predicts worse survival in lung cancer patients. Overexpression of AK4 exaggerates HIF-1α protein expression by increasing intracellular ROS levels and subsequently induces EMT under hypoxia. Attenuation of ROS production with N-acetylcysteine abolishes AK4-induced invasion potential under hypoxia. Pharmacogenomics analysis of the AK4 gene signature revealed that withaferin-A could suppress the AK4-HIF-1α signaling axis and serve as a potent anti-metastatic agent in lung cancer.

Conclusions

Overexpression of AK4 promotes lung cancer metastasis by enhancing HIF-1α stability and EMT under hypoxia. Reversing the AK4 gene signature with withaferin-A may serve as a novel therapeutic strategy to treat metastatic lung cancer.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0698-5) contains supplementary material, which is available to authorized users.

Hypoxia-Induced Resistance to Chemotherapy in Cancer

A major barrier to the successful management of cancer is the development of resistance to therapy. Chemotherapy resistance can either be an intrinsic property of malignant cells developed prior to therapy, or acquired following exposure to anti-cancer drugs. Given the impact of drug resistance to the overall poor survival of cancer patients, there is an urgent need to better understand the molecular pathways regulating this malignant phenotype. In this chapter we describe some of the molecular pathways that contribute to drug resistance in cancer, the role of a microenvironment deficient in oxygen (hypoxia) in malignant progression, and how hypoxia can be a significant factor in the development of drug resistance. We conclude by proposing potential therapeutic approaches that take advantage of a hypoxic microenvironment to chemosensitize therapy-resistant tumours.

Pdgf1aa regulates zebrafish neural crest cells migration through Hif-1 in an oxygen-independent manner

The transcription factor Hif-1α regulates epithelial to mesenchymal transition and neural crest cell chemotaxis in Xenopus. Hif-1α is only stabilised under low oxygen levels, and the in vivo stabilisation of this factor in neural crest cells is poorly understood. Multiple oxygen-independent Hif-1α regulators have been described in cell cultures and cancer models. Among these, the PDGF pathway has been linked to neural crest development. The present study established a connection between the Pdgf pathway and Hif-1α stabilisation in zebrafish. Specifically, embryos with a disrupted Pdgf pathway were rescued by employing hif-1α mRNA through qPCR and immunohistochemistry techniques. The data suggest that oxygen levels in the neural crest are normal and that Pdgf1aa regulates neural crest migration through Hif-1α expression.

Lactate metabolism: historical context, prior misinterpretations, and current understanding

Lactate (La^-) has long been at the center of controversy in research, clinical, and athletic settings. Since its discovery in 1780, La^- has often been erroneously viewed as simply a hypoxic waste product with multiple deleterious effects. Not until the 1980s, with the introduction of the cell-to-cell lactate shuttle did a paradigm shift in our understanding of the role of La^- in metabolism begin. The evidence for La^- as a major player in the coordination of whole-body metabolism has since grown rapidly. La^- is a readily combusted fuel that is shuttled throughout the body, and it is a potent signal for angiogenesis irrespective of oxygen tension. Despite this, many fundamental discoveries about La^- are still working their way into mainstream research, clinical care, and practice. The purpose of this review is to synthesize current understanding of La^- metabolism via an appraisal of its robust experimental history, particularly in exercise physiology. That La^- production increases during dysoxia is beyond debate, but this condition is the exception rather than the rule. Fluctuations in blood [La^-] in health and disease are not typically due to low oxygen tension, a principle first demonstrated with exercise and now understood to varying degrees across disciplines. From its role in coordinating whole-body metabolism as a fuel to its role as a signaling molecule in tumors, the study of La^- metabolism continues to expand and holds potential for multiple clinical applications. This review highlights La^-'s central role in metabolism and amplifies our understanding of past research.

Impact of MicroRNAs in the Cellular Response to Hypoxia

In mammalian cells, hypoxia, or inadequate oxygen availability, regulates the expression of a specific set of MicroRNAs (MiRNAs), termed "hypoxamiRs." Over the past 10 years, the appreciation of the importance of hypoxamiRs in regulating the cellular adaptation to hypoxia has grown dramatically. At the cellular level, each hypoxamiR, including the master hypoxamiR MiR-210, can simultaneously regulate expression of multiple target genes in order to fine-tune the adaptive response of cells to hypoxia. This review addresses the complex molecular regulation of MiRNAs in both physiological and pathological conditions of low oxygen adaptation and the multiple functions of hypoxamiRs in various hypoxia-associated biological processes, including apoptosis, survival, proliferation, angiogenesis, inflammation, and metabolism. From a clinical perspective, we also discuss the potential use of hypoxamiRs as new biomarkers and/or therapeutic targets in cancer and aging-associated diseases including cardiovascular and fibroproliferative disorders.

Lactate as a Signaling Molecule That Regulates Exercise-Induced Adaptations

Lactate (or its protonated form: lactic acid) has been studied by many exercise scientists. The lactate paradigm has been in constant change since lactate was first discovered in 1780. For many years, it was unfairly seen as primarily responsible for muscular fatigue during exercise and a waste product of glycolysis. The status of lactate has slowly changed to an energy source, and in the last two decades new evidence suggests that lactate may play a much bigger role than was previously believed: many adaptations to exercise may be mediated in some way by lactate. The mechanisms behind these adaptations are yet to be understood. The aim of this review is to present the state of lactate science, focusing on how this molecule may mediate exercise-induced adaptations.

Adequate hypoxia inducible factor 1α signaling is indispensable for bone regeneration

Engineered cell-based constructs are an appealing strategy to treat large skeletal defects. However, transplanted cells are often confronted with an environment that is deprived of oxygen and nutrients. Upon hypoxia, most cell types activate hypoxia-inducible factor 1α (HIF-1α) signaling, but its importance for implanted osteoprogenitor cells during bone regeneration is not elucidated. To this end, we specifically deleted the HIF--1α isoform in periosteal progenitor cells and show that activation of HIF-1α signaling in these cells is critical for bone repair by modulating angiogenic and metabolic processes. Activation of HIF-1α is not only crucial for blood vessel invasion, by enhancing angiogenic growth factor production, but also for periosteal cell survival early after implantation, when blood vessels have not yet invaded the construct. HIF-1α signaling limits oxygen consumption to avoid accumulation of harmful ROS and preserve redox balance, and additionally induces a switch to glycolysis to prevent energetic distress. Altogether, our results indicate that the proangiogenic capacity of implanted periosteal cells is HIF-1α regulated and that metabolic adaptations mediate post-implantation cell survival.

Glucose Transporter 1 (SLC2A1) and Vascular Endothelial Growth Factor A (VEGFA) Predict Survival After Resection of Colorectal Cancer Liver Metastasis

OBJECTIVE

To investigate the individual and combined prognostic value of HIF1α, SLC2A1, and vascular endothelial growth factor A (VEGFA) in a multi-institutional cohort of patients with resected colorectal cancer liver metastasis (CRCLM).

BACKGROUND

In the majority of patients with CRCLM, resection seems not to be curative, despite its curative intent. Overexpression of hypoxia-inducible factor 1α (HIF1α), glucose transporter 1 (SLC2A1; also known as GLUT1), and VEGFA has been associated with tumor progression and poor prognosis of patients with colorectal cancer (CRC).

METHODS

Tissue microarrays were generated using CRCLM and patient-matched primary CRC from patients who underwent CRCLM resection between 1990 and 2010. Prognostic value of HIF1α, SLC2A1, and VEGFA was determined by immunohistochemistry. A 500-fold cross-validated hazard rate ratio (HRRav) for overall survival was calculated.

RESULTS

HIF1α, SLC2A1, and VEGFA expression could be evaluated in 328, 350, and 335 patients, respectively. High SLC2A1 expression was associated with good prognosis (HRRav, 0.67; P (HRR >1)  < 0.01) and high VEGFA expression to poor prognosis (HRRav, 1.84; P (HRR < 1)  = 0.02), also after multivariate analysis including established clinicopathological prognostic variables (HRRav, 0.67; P (HRR > 1)  < 0.01 and HRRav, 1.50; P (HRR < 1)  = 0.02, respectively). SLC2A1 showed prognostic value particularly in patients treated with systemic therapy (P < 0.01), whereas the prognostic value of VEGFA expression was mainly observed in patients not treated with systemic therapy (P < 0.01). Prognosis was especially poor in patients with both low SLC2A1 and high VEGFA expression (P < 0.01). HIF1α expression was not associated with survival.

CONCLUSIONS

SLC2A1 and VEGFA expression are prognostic molecular biomarkers for patients with CRCLM with added value to established clinicopathological variables.

Interactions between mitochondrial reactive oxygen species and cellular glucose metabolism

Mitochondrial reactive oxygen species (ROS) production and detoxification are tightly balanced. Shifting this balance enables ROS to activate intracellular signaling and/or induce cellular damage and cell death. Increased mitochondrial ROS production is observed in a number of pathological conditions characterized by mitochondrial dysfunction. One important hallmark of these diseases is enhanced glycolytic activity and low or impaired oxidative phosphorylation. This suggests that ROS is involved in glycolysis (dys)regulation and vice versa. Here we focus on the bidirectional link between ROS and the regulation of glucose metabolism. To this end, we provide a basic introduction into mitochondrial energy metabolism, ROS generation and redox homeostasis. Next, we discuss the interactions between cellular glucose metabolism and ROS. ROS-stimulated cellular glucose uptake can stimulate both ROS production and scavenging. When glucose-stimulated ROS production, leading to further glucose uptake, is not adequately counterbalanced by (glucose-stimulated) ROS scavenging systems, a toxic cycle is triggered, ultimately leading to cell death. Here we inventoried the various cellular regulatory mechanisms and negative feedback loops that prevent this cycle from occurring. It is concluded that more insight in these processes is required to understand why they are (un)able to prevent excessive ROS production during various pathological conditions in humans.

Activating PPARα prevents post-ischemic contractile dysfunction in hypertrophied neonatal hearts

RATIONALE

Post-ischemic contractile dysfunction is a contributor to morbidity and mortality after the surgical correction of congenital heart defects in neonatal patients. Pre-existing hypertrophy in the newborn heart can exacerbate these ischemic injuries, which may partly be due to a decreased energy supply to the heart resulting from low fatty acid β-oxidation rates.

OBJECTIVE

We determined whether stimulating fatty acid β-oxidation with GW7647, a peroxisome proliferator-activated receptor-α (PPARα) activator, would improve cardiac energy production and post-ischemic functional recovery in neonatal rabbit hearts subjected to volume overload-induced cardiac hypertrophy.

METHODS AND RESULTS

Volume-overload cardiac hypertrophy was produced in 7-day-old rabbits via an aorto-caval shunt, after which, the rabbits were treated with or without GW7647 (3 mg/kg per day) for 14 days. Biventricular working hearts were subjected to 35 minutes of aerobic perfusion, 25 minutes of global no-flow ischemia, and 30 minutes of aerobic reperfusion. GW7647 treatment did not prevent the development of cardiac hypertrophy, but did prevent the decline in left ventricular ejection fraction in vivo. GW7647 treatment increased cardiac fatty acid β-oxidation rates before and after ischemia, which resulted in a significant increase in overall ATP production and an improved in vitro post-ischemic functional recovery. A decrease in post-ischemic proton production and endoplasmic reticulum stress, as well as an activation of sarcoplasmic reticulum calcium ATPase isoform 2 and citrate synthase, was evident in GW7647-treated hearts.

CONCLUSIONS

Stimulating fatty acid β-oxidation in neonatal hearts may present a novel cardioprotective intervention to limit post-ischemic contractile dysfunction.

Protective Effects of Inducible HO-1 on Oxygen Toxicity in Rat Brain Endothelial Microvessel Cells

BACKGROUND

Reperfusion in ischemia is believed to generate cytotoxic oxidative stress, which mediates reperfusion injury. These stress conditions can initiate lipid peroxidation and damage to proteins, as well as promote DNA strand breaks. As biliverdin and bilirubin produced by heme oxygenase isoform 1 (HO-1) have antioxidant properties, the production of both antioxidants by HO-1 may help increase the resistance of the ischemic brain to oxidative stress. In the present study, the survival effect of HO-1 was confirmed using hemin.

METHODS

To confirm the roles of HO-1, carbon monoxide, and cyclic guanosine monophosphate further in the antioxidant effect of HO-1 and bilirubin, cells were treated with cycloheximide, desferoxamine, and zinc deuteroporphyrin IX 2,4 bis glycol, respectively.

RESULTS

HO-1 itself acted as an antioxidant. Furthermore, iron, rather than carbon monoxide, was involved in the HO-1-mediated survival effect. HO-1 activity was also important in providing bilirubin as an antioxidant.

CONCLUSION

Our results suggested that HO-1 helped to increase the resistance of the ischemic brain to oxidative stress.

Fatty acid-bearing albumin but not fatty acid-depleted albumin induces HIF-1 activation in human renal proximal tubular epithelial cell line HK-2

Recently, we found that albumin overload induces expression of the transcription factor hypoxia-inducible factor-1α (HIF-1α) protein and several HIF-1 target genes in human renal proximal tubular epithelial cell line HK-2. In this study, the role of albumin-bound fatty acids in the albumin-induced HIF-1 activation was studied. The enhancing effect of fatty acid-bearing human serum albumin [FA(+)HSA] treatment on HIF-1α protein expression was much greater than that of fatty acid-depleted human serum albumin [FA(-)HSA] treatment. The FA(+)HSA treatment induced HIF-1 target gene mRNAs such as those of glucose transporter 1 (GLUT1), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and breast cancer resistance protein (BCRP) in concentration-dependent manners, while FA(-)HSA caused no significant increases in these mRNAs. Consistent with increased GLUT1 mRNA, GLUT1 protein expression and GLUT inhibitor cytochalasin B-sensitive d-[(3)H]glucose uptake activity were significantly enhanced by treatment with FA(+)HSA, but not with FA(-)HSA. These findings indicate that fatty acids bound to albumin play a crucial role in albumin-induced HIF-1 activation followed by changes in HIF-1 target gene expression and protein product activity.

Loss of HIF-1α impairs GLUT4 translocation and glucose uptake by the skeletal muscle cells

Defects in glucose uptake by the skeletal muscle cause diseases linked to metabolic disturbance such as type 2 diabetes. The molecular mechanism determining glucose disposal in the skeletal muscle in response to cellular stimuli including insulin, however, remains largely unknown. The hypoxia-inducible factor-1α (HIF-1α) is a transcription factor operating in the cellular adaptive response to hypoxic conditions. Recent studies have uncovered pleiotropic actions of HIF-1α in the homeostatic response to various cellular stimuli, including insulin under normoxic conditions. Thus we hypothesized HIF-1α is involved in the regulation of glucose metabolism stimulated by insulin in the skeletal muscle. To this end, we generated C2C12 myocytes in which HIF-1α is knocked down by short-hairpin RNA and examined the intracellular signaling cascade and glucose uptake subsequent to insulin stimulation. Knockdown of HIF-1α expression in the skeletal muscle cells resulted in abrogation of insulin-stimulated glucose uptake associated with impaired mobilization of glucose transporter 4 (GLUT4) to the plasma membrane. Such defect seemed to be caused by reduced phosphorylation of the protein kinase B substrate of 160 kDa (AS160). AS160 phosphorylation and GLUT4 translocation by AMP-activated protein kinase activation were abrogated as well. In addition, expression of the constitutively active mutant of HIF-1α (CA-HIF-1α) or upregulation of endogenous HIF-1α in C2C12 cells shows AS160 phosphorylation comparable to the insulin-stimulated level even in the absence of insulin. Accordingly GLUT4 translocation was increased in the cells expressing CA-HIF1α. Taken together, HIF-1α is a determinant for GLUT4-mediated glucose uptake in the skeletal muscle cells thus as a possible target to alleviate impaired glucose metabolism in, e.g., type 2 diabetes.

Mesenchymal stem cell delivery strategies to promote cardiac regeneration following ischemic injury

Myocardial infarction (MI) is one of the leading causes of mortality worldwide and is associated with irreversible cardiomyocyte death and pathological remodeling of cardiac tissue. In the past 15 years, several animal models have been developed for pre-clinical testing to assess the potential of stem cells for functional tissue regeneration and the attenuation of left ventricular remodeling. The promising results obtained in terms of improved cardiac function, neo-angiogenesis and reduction in infarct size have motivated the initiation of clinical trials in humans. Despite the potential, the results of these studies have highlighted that the effective delivery and retention of viable cells within the heart remain significant challenges that have limited the therapeutic efficacy of cell-based therapies for treating the ischemic myocardium. In this review, we discuss key elements for designing clinically translatable cell-delivery approaches to promote myocardial regeneration. Key topics addressed include cell selection, with a focus on mesenchymal stem cells derived from the bone marrow (bMSCs) and adipose tissue (ASCs), including a discussion of their potential mechanisms of action. Natural and synthetic biomaterials that have been investigated as injectable cell delivery vehicles for cardiac applications are critically reviewed, including an analysis of the role of the biomaterials themselves in the therapeutic scheme.

Crosstalk between Mdm2, p53 and HIF1-α: distinct responses to oxygen stress and implications for tumour hypoxia

The E3 ubiquitin ligase Mdm2 regulates two transcription factors, p53 and HIF1α, which appear to be tailored towards different and specific roles within the cell, the DNA damage and hypoxia responses, respectively. However, evidence increasingly points towards the interplay between these factors being crucial for the regulation of cellular metabolism and survival in times of oxygen stress, which has particular relevance for tumour formation. Mdm2, p53 and HIF1α all respond to hypoxia, and intriguingly, have distinct roles depending on the level of hypoxia. The data from numerous studies across different conditions hint at the interplay between these key factors in cellular homeostasis. Here we try to weave these strands together, to create a picture of the complex tapestry of interactions that demonstrates the importance of the crosstalk between these key regulatory proteins during hypoxia.

Reciprocal regulation of HIF-1α and lincRNA-p21 modulates the Warburg effect

Hypoxia has long been linked to the Warburg effect, yet the underlying mechanism remains largely unclear. It is also not known if lncRNAs are involved in the contribution of hypoxia to the Warburg effect. Here we show that lincRNA-p21 is a hypoxia-responsive lncRNA and is essential for hypoxia-enhanced glycolysis. Hypoxia/HIF-1α-induced lincRNA-p21 is able to bind HIF-1α and VHL and thus disrupts the VHL-HIF-1α interaction. This disassociation attenuates VHL-mediated HIF-1α ubiquitination and causes HIF-1α accumulation. These data indicate the existence of a positive feedback loop between HIF-1α and lincRNA-p21 that promotes glycolysis under hypoxia. The ability of lincRNA-p21 to promote tumor growth is validated in mouse xenograft models. Together, these findings suggest that lincRNA-p21 is an important player in the regulation of the Warburg effect and also implicate lincRNA-p21 as a valuable therapeutic target for cancer.

Fundamental role for HIF-1α in constitutive expression of human β defensin-1

Antimicrobial peptides are secreted by the intestinal epithelium to defend from microbial threats. The role of human β defensin-1 (hBD-1) is notable because its gene (beta-defensin 1 (DEFB1)) is constitutively expressed and its antimicrobial activity is potentiated in the low-oxygen environment that characterizes the intestinal mucosa. Hypoxia-inducible factor (HIF) is stabilized even in healthy intestinal mucosa, and we identified that epithelial HIF-1α maintains expression of murine defensins. Extension to a human model revealed that basal HIF-1α is critical for the constitutive expression of hBD-1. Chromatin immunoprecipitation identified HIF-1α binding to a hypoxia response element in the DEFB1 promoter whose importance was confirmed by site-directed mutagenesis. We used 94 human intestinal samples to identify a strong expression correlation between DEFB1 and the canonical HIF-1α target GLUT1. These findings indicate that basal HIF-1α is critical for constitutive expression of enteric DEFB1 and support targeting epithelial HIF for restoration and maintenance of intestinal integrity.

Hypoxia-inducible factor 1 and cardiovascular disease

Cardiac function is required for blood circulation and systemic oxygen delivery. However, the heart has intrinsic oxygen demands that must be met to maintain effective contractility. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that functions as a master regulator of oxygen homeostasis in all metazoan species. HIF-1 controls oxygen delivery, by regulating angiogenesis and vascular remodeling, and oxygen utilization, by regulating glucose metabolism and redox homeostasis. Analysis of animal models suggests that by activation of these homeostatic mechanisms, HIF-1 plays a critical protective role in the pathophysiology of ischemic heart disease and pressure-overload heart failure.

Hypoxia regulates FGFR3 expression via HIF-1α and miR-100 and contributes to cell survival in non-muscle invasive bladder cancer

BACKGROUND

Non-muscle invasive (NMI) bladder cancer is characterised by increased expression and activating mutations of FGFR3. We have previously investigated the role of microRNAs in bladder cancer and have shown that FGFR3 is a target of miR-100. In this study, we investigated the effects of hypoxia on miR-100 and FGFR3 expression, and the link between miR-100 and FGFR3 in hypoxia.

METHODS

Bladder cancer cell lines were exposed to normoxic or hypoxic conditions and examined for the expression of FGFR3 by quantitative PCR (qPCR) and western blotting, and miR-100 by qPCR. The effect of FGFR3 and miR-100 on cell viability in two-dimensional (2-D) and three-dimensional (3-D) was examined by transfecting siRNA or mimic-100, respectively.

RESULTS

In NMI bladder cancer cell lines, FGFR3 expression was induced by hypoxia in a transcriptional and HIF-1α-dependent manner. Increased FGFR3 was also in part dependent on miR-100 levels, which decreased in hypoxia. Knockdown of FGFR3 led to a decrease in phosphorylation of the downstream kinases mitogen-activated protein kinase (MAPK) and protein kinase B (PKB), which was more pronounced under hypoxic conditions. Furthermore, transfection of mimic-100 also decreased phosphorylation of MAPK and PKB. Finally, knocking down FGFR3 profoundly decreased 2-D and 3-D cell growth, whereas introduction of mimic-100 decreased 3-D growth of cells.

CONCLUSION

Hypoxia, in part via suppression of miR-100, induces FGFR3 expression in bladder cancer, both of which have an important role in maintaining cell viability under conditions of stress.

Hypoxia regulates FGFR3 expression via HIF-1α and miR-100 and contributes to cell survival in non-muscle invasive bladder cancer

BACKGROUND

Non-muscle invasive (NMI) bladder cancer is characterised by increased expression and activating mutations of FGFR3. We have previously investigated the role of microRNAs in bladder cancer and have shown that FGFR3 is a target of miR-100. In this study, we investigated the effects of hypoxia on miR-100 and FGFR3 expression, and the link between miR-100 and FGFR3 in hypoxia.

METHODS

Bladder cancer cell lines were exposed to normoxic or hypoxic conditions and examined for the expression of FGFR3 by quantitative PCR (qPCR) and western blotting, and miR-100 by qPCR. The effect of FGFR3 and miR-100 on cell viability in two-dimensional (2-D) and three-dimensional (3-D) was examined by transfecting siRNA or mimic-100, respectively.

RESULTS

In NMI bladder cancer cell lines, FGFR3 expression was induced by hypoxia in a transcriptional and HIF-1α-dependent manner. Increased FGFR3 was also in part dependent on miR-100 levels, which decreased in hypoxia. Knockdown of FGFR3 led to a decrease in phosphorylation of the downstream kinases mitogen-activated protein kinase (MAPK) and protein kinase B (PKB), which was more pronounced under hypoxic conditions. Furthermore, transfection of mimic-100 also decreased phosphorylation of MAPK and PKB. Finally, knocking down FGFR3 profoundly decreased 2-D and 3-D cell growth, whereas introduction of mimic-100 decreased 3-D growth of cells.

CONCLUSION

Hypoxia, in part via suppression of miR-100, induces FGFR3 expression in bladder cancer, both of which have an important role in maintaining cell viability under conditions of stress.

Hypoxia-inducible factor-1 (HIF-1): a potential target for intervention in ocular neovascular diseases

Constant oxygen supply is essential for proper tissue development, homeostasis and function of all eukaryotic organisms. Cellular response to reduced oxygen levels is mediated by the transcriptional regulator hypoxia-inducible factor-1 (HIF-1). It is a heterodimeric complex protein consisting of an oxygen dependent subunit (HIF-1α) and a constitutively expressed nuclear subunit (HIF-1β). In normoxic conditions, de novo synthesized cytoplasmic HIF-1α is degraded by 26S proteasome. Under hypoxic conditions, HIF-1α is stabilized, binds with HIF-1β and activates transcription of various target genes. These genes play a key role in regulating angiogenesis, cell survival, proliferation, chemotherapy, radiation resistance, invasion, metastasis, genetic instability, immortalization, immune evasion, metabolism and stem cell maintenance. This review highlights the importance of hypoxia signaling in development and progression of various vision threatening pathologies such as diabetic retinopathy, retinopathy of prematurity, age-related macular degeneration and glaucoma. Further, various inhibitors of HIF-1 pathway that may have a viable potential in the treatment of oxygen-dependent ocular diseases are also discussed.

Differentiated embryonic chondrocyte-expressed gene 1 is associated with hypoxia-inducible factor 1α and Ki67 in human gastric cancer

Background

Gastric cancer is a leading causes of cancer-related deaths ,but the underlying molecular mechanisms of its progression are largely unknown. Differentiated embryonic chondrocyte-expressed gene 1 (DEC1), is an important transcription factor involved in the progression of tumors and has recently been identified to be strongly inducible by hypoxia. Little is known about the contribution of DEC1 to the intracellular hypoxia and proliferation signaling events in gastric cancer.

Methods

Immunohistochemistry was used to detect the expression of DEC1, hypoxia-inducible factor 1(HIF-1α) and Ki67 in 173 human gastric cancer samples and adjacent non-tumor tissues samples. The relationship between DEC1, HIF-1α and Ki67 was evaluated.

Results

DEC1 protein was persistently expressed in the nucleus and cytoplasm of gastric cancer tissue. The protein expression of DEC1 and HIF-1α in tumour tissues was 83.8% and 54.3%, respectively, and was significantly higher than that in adjacent normal tissues (83.8% vs 23.7%, P <0.001; 54.3% vs 12.7%, P< 0.001). The expression of DEC1 and HIF-1α was associated with poor histological differentiation. (P < 0. 01). Furthermore, DEC1 level was positively correlated with HIF-1α (P < 0. 01, r=0.290) and Ki67 expression (P < 0. 01, r=0.249).

Conclusion

The upregulation of DEC1 may play an important role in hypoxia regulation and cell proliferation in gastric cancer. The relevant molecular mechanism requires further investigation.

Virtual Slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1794565980889391med.motic.com/MoticGallery/Slide?id=08d180cd-5fdb-4cee-830a-0b1fef3311f2&user=2C69F0D6-A478-4A2B-ABF0-BB36763E8025med.motic.com/MoticGallery/Slide?id=4762991d-3f2f-43aa-b4bf-ecdd2c2ae3ec&user=2C69F0D6-A478-4A2B-ABF0-BB36763E8025med.motic.com/MoticGallery/Slide?id=2717f209-b3fd-4e71-b621-0d60ea507a82&user=2C69F0D6-A478-4A2B-ABF0-BB36763E8025

HIF- and non-HIF-regulated hypoxic responses require the estrogen-related receptor in Drosophila melanogaster

Low-oxygen tolerance is supported by an adaptive response that includes a coordinate shift in metabolism and the activation of a transcriptional program that is driven by the hypoxia-inducible factor (HIF) pathway. The precise contribution of HIF-1a in the adaptive response, however, has not been determined. Here, we investigate how HIF influences hypoxic adaptation throughout Drosophila melanogaster development. We find that hypoxic-induced transcriptional changes are comprised of HIF-dependent and HIF-independent pathways that are distinct and separable. We show that normoxic set-points of carbohydrate metabolites are significantly altered in sima mutants and that these animals are unable to mobilize glycogen in hypoxia. Furthermore, we find that the estrogen-related receptor (dERR), which is a global regulator of aerobic glycolysis in larvae, is required for a competent hypoxic response. dERR binds to dHIFa and participates in the HIF-dependent transcriptional program in hypoxia. In addition, dERR acts in the absence of dHIFa in hypoxia and a significant portion of HIF-independent transcriptional responses can be attributed to dERR actions, including upregulation of glycolytic transcripts. These results indicate that competent hypoxic responses arise from complex interactions between HIF-dependent and -independent mechanisms, and that dERR plays a central role in both of these programs.

When oxygen levels fall below normal, cells are said to be in a hypoxic state. Once in hypoxia, dramatic changes are induced that allow for adaptation. In particular, energetic metabolism and transcription are highly affected. HIF (hypoxia inducible factor) is a highly conserved factor that is the driving force behind many hypoxia-induced changes—it is inactive in normal conditions and becomes active in hypoxia. Using the fruit fly as a model system, we show that hypoxic responses consist of HIF and non-HIF-dependent pathways. These response programs counteract the impacts of low oxygen by broadly influencing different cellular processes such as the breakdown of sugars, but only at appropriate developmental times. We provide evidence that HIF- and non-HIF-dependent pathways are complemented by the actions of the steroid hormone receptor estrogen-related receptor (ERR), which we show is also essential in hypoxia. Our results place new emphasis on the actions of HIF and suggest that alternative HIF-independent pathways play a more prominent role than previously thought.

Strategies To Assess Hypoxic/HIF-1-Active Cancer Cells for the Development of Innovative Radiation Therapy

Local tumor recurrence and distant tumor metastasis frequently occur after radiation therapy and result in the death of cancer patients. These problems are caused, at least in part, by a tumor-specific oxygen-poor microenvironment, hypoxia. Oxygen-deprivation is known to inhibit the chemical ionization of both intracellular macro-molecules and water, etc., and thus reduce the cytotoxic effects of radiation. Moreover, DNA damage produced by free radicals is known to be more repairable under hypoxia than normoxia. Hypoxia is also known to induce biological tumor radioresistance through the activation of a transcription factor, hypoxia-inducible factor 1 (HIF-1). Several potential strategies have been devised in radiation therapy to overcome these problems; however, they have not yet achieved a complete remission. It is essential to reveal the intratumoral localization and dynamics of hypoxic/HIF-1-active tumor cells during tumor growth and after radiation therapy, then exploit the information to develop innovative therapeutic strategies, and finally damage radioresistant cells. In this review, we overview problems caused by hypoxia/HIF-1-active cells in radiation therapy for cancer and introduce strategies to assess intratumoral hypoxia/HIF-1 activity.

Old proteins - new locations: myoglobin, haemoglobin, neuroglobin and cytoglobin in solid tumours and cancer cells

AIM

The unexpected identification of myoglobin (MB) in breast cancer prompted us to evaluate the clinico-pathological value of MB, haemoglobin (HB) and cytoglobin (CYGB) in human breast carcinoma cases. We further screened for the presence of neuroglobin (NGB) and CYGB in tumours of diverse origin, and assessed the O(2) -response of HB, MB and CYGB mRNAs in cancer cell lines, to better elicit the links between this ectopic globin expression and tumour hypoxia.

METHODS

Breast tumours were analysed by immunohistochemistry for HB, MB and CYGB and correlated with clinico-pathological parameters. Screening for CYGB and NGB mRNA expression in tumour entities was performed by hybridization, quantitative PCR (qPCR) and bioinformatics. Hypoxic or anoxic responses of HB, MB and CYGB mRNAs was analysed by qPCR in human Hep3B, MCF7, HeLa and RCC4 cancer cell lines.

RESULTS

78.8% of breast cancer cases were positive for MB, 77.9% were positive for HB and 55.4% expressed CYGB. The closest correlation with markers of hypoxia was observed for CYGB. Compared to the weakly positive status of MB in healthy breast tissues, invasive tumours either lost or up-regulated MB. Breast carcinomas showed the tendency to silence CYGB. HB was not seen in normal tissues and up-regulated in tumours. Beyond breast malignancies, expression levels of NGB and CYGB mRNAs were extremely low in brain tumours (glioblastoma, astrocytoma). NGB was not observed in non-brain tumours. CYGB mRNA, readily detectable in breast cancer and other tumours, is down-regulated in lung adenocarcinomas. Alpha1 globin (α1 globin) and Mb were co-expressed in MCF7 and HeLa cells; CYGB transcription was anoxia-inducible in Hep3B and RCC4 cells.

CONCLUSIONS

This is the first time that HB and CYGB are reported in breast cancer. Neither NGB nor CYGB are systematically up-regulated in tumours. The down-regulated CYGB expression in breast and lung tumours is in line with a tumour-suppressor role. Each of the screened cancer cells expresses at least one globin (i.e. main globin species: CYGB in Hep3B; α1 globin + MB in MCF7 and HeLa). Thus, globins exist in a wide variety of solid tumours. However, the generally weak expression of the endogenous proteins in the cancer argues against a significant contribution to tumour oxygenation. Future studies should consider that cancer-expressed globins might function in ways not directly linked to the binding and transport of oxygen.

Oxygen homeostasis

Metazoan life is dependent upon the utilization of O(2) for essential metabolic processes and oxygen homeostasis is an organizing principle for understanding metazoan evolution, ontology, physiology, and pathology. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that is expressed by all metazoan species and functions as a master regulator of oxygen homeostasis. Recent studies have elucidated complex mechanisms by which HIF-1 activity is regulated and by which HIF-1 regulates gene expression, with profound consequences for prenatal development, postnatal physiology, and disease pathogenesis.

Hypoxia-inducible factor-dependent production of profibrotic mediators by hypoxic Kupffer cells

AIM

Liver fibrosis develops when chronic liver injury stimulates cells in the liver to produce mediators that activate hepatic stellate cells and stimulate them to secrete collagen. Recent studies suggest that the hypoxia-regulated transcription factor, hypoxia-inducible factor-1alpha, is essential for upregulation of profibrotic mediators, such as platelet-derived growth factor, in the liver during the development of liver fibrosis. What remains unknown, however, is the cell type-specific regulation of profibrotic mediators by hypoxia-inducible factors. Accordingly, in the present study the hypothesis tested was that hypoxia-inducible factors regulate production of profibrotic mediators by hypoxic Kupffer cells.

METHODS

Kupffer cells were isolated from control mice and hypoxia-inducible factor-1beta-deficient mice and exposed to room air or 1% oxygen (i.e. hypoxia). Levels of profibrotic mediators were quantified by real-time polymerase chain reaction.

RESULTS

Exposure of Kupffer cells isolated from control mice to 1% oxygen activated hypoxia-inducible factor-1alpha, and increased mRNA levels of platelet-derived growth factor-B, vascular endothelial growth factor, angiopoietin-1 and monocyte chemotactic protein-1. Upregulation of all of these mediators by hypoxia was prevented in Kupffer cells isolated from hypoxia-inducible factor-1beta-deficient mice.

CONCLUSION

RESULTS from these studies suggest that hypoxia-inducible factors are critical regulators of profibrotic mediator production by hypoxic Kupffer cells.

High glucose activates HIF-1-mediated signal transduction in glomerular mesangial cells through a carbohydrate response element binding protein

High glucose evokes a variety of signals in mesangial cells that alter cellular functions responsible for the development of diabetic glomerulopathy. The hypoxia-inducible factor-1alpha (HIF-1alpha) regulates cellular homeostasis under hypoxic conditions, but it also has pleiotropic effects in response to cellular stresses at normoxia. Here we determined whether HIF-1alpha has a role in the regulation of mesangial cells in hyperglycemia. In the streptozotocin-induced diabetic mouse model, glomerular mesangial cells had a significant increase in HIF-1alpha expression in the nucleus. In cultured mesangial cells, high glucose enhanced the expression of HIF-1alpha and its target genes known to be involved in the development of diabetic glomerulopathy. A glucose-responsive carbohydrate response element binding protein (ChREBP) was found to have a critical role in the transcriptional upregulation of HIF-1alpha and downstream gene expression in mesangial cells exposed to high glucose. Knockdown of HIF-1alpha or ChREBP in mesangial cells abrogated the high glucose-mediated perturbation of gene expression. Our results show that ChREBP and HIF-1alpha mediate gene regulation in mesangial cells. Further studies will be needed to find out whether these findings are relevant to the development of the diabetic nephropathy.

Diminished carcinogen detoxification is a novel mechanism for hypoxia-inducible factor 1-mediated genetic instability

The hypoxia-inducible factor 1 (HIF-1) pathway is induced in many tumors and associated with poorer outcome. The hypoxia-responsive transcription factor HIF-1alpha dimerizes with the aryl hydrocarbon receptor nuclear translocator (ARNT), which is also an important binding partner for the aryl hydrocarbon receptor (AhR). AhR is an important mediator in the metabolic activation and detoxification of carcinogens, such as the environmental pollutant benzo[a]pyrene (BaP). We hypothesized that HIF-1alpha activation attenuates BaP-induced AhR-mediated gene expression, which may lead to increased genetic instability and malignant progression. Human lung carcinoma cells (A549) were simultaneously stimulated with CoCl(2), which leads to HIF-1alpha stabilization and varying concentrations of BaP. Both quantitative PCR and immunoblot analysis indicated that induction of the hypoxia response pathway significantly reduced the levels of AhR downstream targets CYP1A1 and CYP1B1 and AhR protein binding to ARNT. We further demonstrate that the BaP-induced hypoxanthine-guanine phosphoribosyltransferase mutation frequency and gamma-H2AX foci were markedly amplified when the HIF-1 pathway was induced. BaP-DNA adducts were only marginally increased, and transient strand breaks were diminished by HIF-1 induction, indicating changes in DNA repair. These data indicate that concurrent exposure of tumor cells to hypoxia and exogenous genotoxins can enhance genetic instability.

Role of the HBx oncoprotein in carbonic anhydrase 9 induction

Carbonic anhydrase 9 (CA9), as one of the most hypoxia-responsive genes, has been associated almost exclusively with hypoxic tumors. Its principal role is in pH regulation which helps tumor cells overcome intracellular acidosis and survive extended periods of time with low oxygen. Hypoxia-inducible factor 1 (HIF-1) is the main transcriptional activator of CA9. Hepatitis B virus X protein (HBx) has been shown to increase the transcriptional activity of HIF-1. HBx is often expressed from the gene integrated in the hepatocytes infected persistently and contributes significantly to alterations in host gene expression that can lead to the development of hepatocellular carcinoma (HCC) associated with Hepatitis B virus (HBV). The aim of this study was to determine the effect of HBx on expression of CA9. Transient transfection of HBx led to an increase in the expression of CA9 as assessed by RT-PCR and Western blotting. HBx was able to increase CA9 promoter activity significantly in several cell lines. The effect was mediated via HIF-1 and a functional HRE element located -10/-3 bp upstream of the CA9 transcription initiation site. These data suggest that CA9 may be involved in the development of HCC by contributing to the survival of hepatocytes infected with HBV in liver tissue with fibrosis.

Effect of hypoxia and exogenous IL-10 on the pro-inflammatory cytokine TNF-alpha and the anti-angiogenic molecule soluble Flt-1 in placental villous explants

INTRODUCTION

The placenta plays a pivotal role in the pathophysiology of preeclampsia. Insufficient trophoblast invasion within the placenta can cause focal regions of ischaemia/hypoxia that, in turn, may stimulate the production of inflammatory cytokines. These cytokines are thought to cause endothelial cell activation and dysfunction, resulting in the clinical signs of preeclampsia. In addition to insufficient trophoblast invasion, the presence of inadequate maternal vasculature remodelling by trophoblasts also leads to changes in angiogenesis that may result from variations in the inflammatory cytokine profile.

AIMS

This study examined changes in the protein levels of IL-10 (immunoregulatory), TNF-alpha (pro-inflammatory) and sFlt-1 (anti-angiogenic) in normal term placentas under different oxygen tensions. The second aim was to determine if the link between varying levels of the cytokine, IL-10, and the expression/release of TNF-alpha was oxygen dependent, and whether there was a concurrent change in sFlt-1.

METHODS

Normal term placentas (n=6) were cultured at three different oxygen tensions (2%, 8% or 21%) in the presence or absence of exogenous IL-10. Protein (TNF-alpha and sFlt-1) secretion was measured using commercial ELISA kits, and qRT-PCR was used to examine gene expression.

RESULTS

Placental IL-10 release was significantly reduced at 2% oxygen when compared to 8% (p=0.045) and 21% (p=0.013). Expression of TNF-alpha and sFlt-1 was not significantly different. Exogenous IL-10 significantly reduced TNF-alpha protein levels only when explants were cultured in 2% oxygen (p=0.05). Soluble Flt-1 protein secretion was unaffected by the addition of IL-10 at any of the oxygen tensions tested.

CONCLUSION

TNF-alpha release can be inhibited in vitro by IL-10 under hypoxic conditions. However, IL-10 has no affect on sFlt-1 in term placentas, suggesting that these molecules act either via different pathways, or if linked, may be so at different stages of placental development.