Cobalt chloride and low oxygen tension trigger differentiation of acute myeloid leukemic cells: possible mediation of hypoxia-inducible factor-1alpha

The hypoxia signaling pathway in the development of acute myeloid leukemia

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. Although advances in targeted agents have greatly improved the prognosis of patients with AML in recent years, those who fail to achieve remission or relapse after remission are still in urgent need of novel therapeutic strategies. The hypoxia signaling pathway is involved in various biological processes, and hypoxia-inducible factor alpha (HIF-α) is considered a potential therapeutic target in AML. The bone marrow microenvironment is known to be in a state of chronic hypoxia, which is important for hematopoietic stem cells to maintain quiescence, and provides leukemic stem cells with a refuge from immune defenses and chemotherapeutic agents. Therefore, this review aims to explore the role of the HIF-α signaling pathway in the development of AML.

Hypoxia and Hypoxia Mimetic Agents As Potential Priming Approaches to Empower Mesenchymal Stem Cells

Mesenchymal stem cells (MSC) exhibit self-renewal capacity and multilineage differentiation potential, making them attractive for research and clinical application. The properties of MSC can vary depending on specific micro-environmental factors. MSC resides in specific niches with low oxygen concentrations, where oxygen functions as a metabolic substrate and a signaling molecule. Conventional physical incubators or chemically hypoxia mimetic agents are applied in cultures to mimic the original low oxygen tension settings where MSC originated. This review aims to focus on the current knowledge of the effects of various physical hypoxic conditions and widely used hypoxia-mimetic agents-PHD inhibitors on mesenchymal stem cells at a cellular and molecular level, including proliferation, stemness, differentiation, viability, apoptosis, senescence, migration, immunomodulation behaviors, as well as epigenetic changes.

In Vitro Tumor Mimetic Spheroid Model: Void Space within a Self-Detachable Cross-Linked Hydrogel

The three-dimensional (3D) spheroid cell culture model is crucial in screening anticancer drugs in vitro and understanding tumor cell behavior. However, the current in vitro models require highly skilled techniques. Here, we present an in vitro, tumor-mimetic, self-detachable, cancer cell spheroid model that provides the confined space of a tumor microenvironment, convenient spheroid retrieval, immunostaining, treatment, and imaging. We formed a void space within alginate macrobeads by ionic disintegration at a specific region inside. The macrobeads were further destabilized with bovine serum albumin to retrieve the spheroid cultured within the void space. Quantitative analysis of the immunofluorescence images of the cultured spheroids showed enhanced expressions of the hypoxia-inducible factor-1α (HIF-1α) and carbonic anhydrase-9 (CA-9), like monolayer cultures of cancer cells under hypoxic conditions (0.2% oxygen). Furthermore, adding CoCl2 to the cell culture media induces even higher amounts of HIF-1α and CA-9 in the cultured spheroids. In conclusion, the present work highlighted the in vitro spheroid model, which is closer to the tumor microenvironment and has user-friendly cell seeding, spheroid retrieval, and immunostaining steps.

AhR and HIF-1α Signaling Pathways in Benign Meningioma under Hypoxia

The role of hypoxia in benign meningiomas is less clear than that in the malignant meningiomas. Hypoxia-induced transcription factor 1 subunit alpha (HIF-1α) and its downstream signaling pathways play a central role in the mechanism of hypoxia. HIF-1α forms a complex with the aryl hydrocarbon receptor nuclear translocator (ARNT) protein and can compete for ARNT with aryl hydrocarbon receptor (AhR). In this work, the status of HIF-1α- and AhR-dependent signaling pathways was investigated in World Health Organization (WHO) grade 1 meningioma and patient-derived tumor primary cell culture under hypoxic conditions. mRNA levels of HIF-1α, AhR, and of their target genes as well as of ARNT and nuclear receptor coactivator NCOA2 were determined in tumor tissues from patients in whom the tumor was promptly removed either with or without prior endovascular embolization. Using the patient-derived nonembolized tumor primary cell culture, the effects of a hypoxia mimetic cobalt chloride (CoCl₂) and an activator of the AhR signaling pathway benzo(α)pyrene (B[a]P) on mRNA levels of HIF-1α, AhR, and their target genes were investigated. Our findings show active functioning of AhR signaling in meningioma tissue of patients with tumor embolization and crosstalk between HIF-1α and AhR signaling in meningeal cells under hypoxia.

Aryl Hydrocarbon Receptor Agonism Antagonizes the Hypoxia-driven Inflammation in Cystic Fibrosis

Hypoxia contributes to the exaggerated yet ineffective airway inflammation that fails to oppose infections in cystic fibrosis (CF). However, the potential for impairment of essential immune functions by HIF-1α (hypoxia-inducible factor 1α) inhibition demands a better comprehension of downstream hypoxia-dependent pathways that are amenable for manipulation. We assessed here whether hypoxia may interfere with the activity of AhR (aryl hydrocarbon receptor), a versatile environmental sensor highly expressed in the lungs, where it plays a homeostatic role. We used murine models of Aspergillus fumigatus infection in vivo and human cells in vitro to define the functional role of AhR in CF, evaluate the impact of hypoxia on AhR expression and activity, and assess whether AhR agonism may antagonize hypoxia-driven inflammation. We demonstrated that there is an important interferential cross-talk between the AhR and HIF-1α signaling pathways in murine and human CF, in that HIF-1α induction squelched the normal AhR response through an impaired formation of the AhR:ARNT (aryl hydrocarbon receptor nuclear translocator)/HIF-1β heterodimer. However, functional studies and analysis of the AhR genetic variability in patients with CF proved that AhR agonism could prevent hypoxia-driven inflammation, restore immune homeostasis, and improve lung function. This study emphasizes the contribution of environmental factors, such as infections, in CF disease progression and suggests the exploitation of hypoxia:xenobiotic receptor cross-talk for antiinflammatory therapy in CF.

Ginkgo biloba Golden Leaf Extract (GGLE) Inhibits Melanoma Cell Invasion and Angiogenesis Through Inhibition of Angiogenin

The popular dietary supplements of Ginkgo biloba (Ginkgo) products have been reported to have anti-cancer activities in multiple cellular and animal studies, with the benefits yet to be proven with clinical trials. The mechanisms of action are not clear, forming a barrier to investigation in Gingko-specific benefits to cancer patients, especially when combined with other therapies. Here we reported on the discovery of a novel mechanism by which a Ginkgo golden leaf extract (GGLE) inhibited melanoma cell invasion and angiogenesis. GGLE did not inhibit melanoma cells via direct cytotoxicity. Instead, GGLE significantly inhibited total RNase activities in melanoma cells under both normoxia and hypoxia conditions. The RNase angiogenin was induced twofolds by hypoxia, and the induction was significantly suppressed by GGLE treatment in a dose dependent manner. As a result of angiogenin inhibition, GGLE inhibited melanoma cell migration and invasion in a dose dependent manner. Conditioned media from melanoma cell culture sufficiently induced in vitro angiogenesis in human endothelial cells, whereas the conditioned media of GGLE-treated melanoma cells significantly inhibited this angiogenetic activity. This was accompanied with markedly reduced angiogenin concentrations in the GGLE-treated melanoma cell conditioned media. We concluded that, instead of direct cytotoxicity, GGLE inhibited angiogenin synthesis and secretion by melanoma cells, resulting in inhibition of tumor cell invasion and tumor-induced angiogenesis. This new mechanism opens the door for investigation in GGLE influencing tumor microenvironment, and warrants further investigation and validation in vivo.

RUNX Family in Hypoxic Microenvironment and Angiogenesis in Cancers

The tumor microenvironment (TME) is broadly implicated in tumorigenesis, as tumor cells interact with surrounding cells to influence the development and progression of the tumor. Blood vessels are a major component of the TME and are attributed to the creation of a hypoxic microenvironment, which is a common feature of advanced cancers and inflamed premalignant tissues. Runt-related transcription factor (RUNX) proteins, a transcription factor family of developmental master regulators, are involved in vital cellular processes such as differentiation, proliferation, cell lineage specification, and apoptosis. Furthermore, the RUNX family is involved in the regulation of various oncogenic processes and signaling pathways as well as tumor suppressive functions, suggesting that the RUNX family plays a strategic role in tumorigenesis. In this review, we have discussed the relevant findings that describe the crosstalk of the RUNX family with the hypoxic TME and tumor angiogenesis or with their signaling molecules in cancer development and progression.

The Effect of the Classical TSPO Ligand PK 11195 on In Vitro Cobalt Chloride Model of Hypoxia-like Condition in Lung and Brain Cell Lines

The mitochondrial translocator protein (TSPO) is a modulator of the apoptotic pathway involving reactive oxygen species (ROS) generation, mitochondrial membrane potential (Δψm) collapse, activation of caspases, and eventually initiation of the apoptotic process. In this in vitro study, H1299 lung cells and BV-2 microglial cells were exposed to the hypoxia-like effect of CoCl2 with or without PK 11195. Exposing the H1299 cells to 0.5 mM CoCl2 for 24 h resulted in decreases in cell viability (63%, p < 0.05), elevation of cardiolipin peroxidation levels (38%, p < 0.05), mitochondrial membrane potential depolarization (13%, p < 0.001), and apoptotic cell death (117%, p < 0.05). Pretreatment with PK 11195 (25 µM) exhibited significant protective capacity on CoCl2-induced alterations in the mentioned processes. Exposure of BV-2 cells to increasing concentrations of CoCl2 (0.3, 0.5, 0.7 mM) for 4 h resulted in alterations in the same cellular processes. These alterations were obtained in a dose-dependent manner, except the changes in caspases 3 and 9. The novel ligands as well as PK 1195 attenuated the in vitro hypoxia-like effects of CoCl2. It appears that the TSPO ligand PK 11195 can prevent CoCl2-induced cellular damage in both non-neuronal and brain cell lines, and they may offer a novel approach to the treatment of hypoxia-related lung and brain diseases in some cases that fail to respond to conventional therapies.

Molecular and Cellular Response of the Myocardium (H9C2 Cells) Towards Hypoxia and HIF-1α Inhibition

Introduction

Oxidative phosphorylation is an essential feature of Animalian life. Multiple adaptations have developed to protect against hypoxia, including hypoxia-inducible-factors (HIFs). The major role of HIFs may be in protecting against oxidative stress, not the preservation of high-energy phosphates. The precise mechanism(s) of HIF protection is not completely understood.

Materials and Methods

To better understand the role of hypoxia-inducible-factor-1, we exposed heart/myocardium cells (H9c2) to both normoxia and hypoxia, as well as cobalt chloride (prolyl hydroxylase inhibitor), echniomycin (HIF inhibitor), A2P (anti-oxidant), and small interfering RNA to beclin-1. We measured cell viability, intracellular calcium and adenosine triphosphate, NADP/NADPH ratios, total intracellular reactive oxidative species levels, and markers of oxidative and antioxidant levels measured.

Results

Hypoxia (1%) leads to increased intracellular Ca2+ levels, and this response was inhibited by A2P and echinomycin (ECM). Exposure of H9c2 cells to hypoxia also led to an increase in both mRNA and protein expression for Cav 1.2 and Cav 1.3. Exposure of H9c2 cells to hypoxia led to a decrease in intracellular ATP levels and a sharp reduction in total ROS, SOD, and CAT levels. The impact of hypoxia on ROS was reversed with HIF-1 inhibition through ECM. Exposure of H9c2 cells to hypoxia led to an increase in Hif1a, VEGF and EPO protein expression, as well as a decrease in mitochondrial DNA. Both A2P and ECM attenuated this response to varying degrees.

Conclusion

Hypoxia leads to increased intracellular Ca2+, and inhibition of HIF-1 attenuates the increase in intracellular Ca2+ that occurs with hypoxia. HIF-1 expression leads to decreased adenosine triphosphate levels, but the role of HIF-1 on the production of reactive oxidative species remains uncertain. Anti-oxidants decrease HIF-1 expression in the setting of hypoxia and attenuate the increase in Ca2+ that occurs during hypoxia (with no effect during normoxia). Beclin-1 appears to drive autophagy in the setting of hypoxia (through ATG5) but not in normoxia. Additionally, Beclin-1 is a powerful driver of reactive oxidative species production and plays a role in ATP production. HIF-1 inhibition does not affect autophagy in the setting of hypoxia, suggesting that there are other drivers of autophagy that impact beclin-1.

Hypoxia as a Modulator of Inflammation and Immune Response in Cancer

A clear association between hypoxia and cancer has heretofore been established; however, it has not been completely developed. In this sense, the understanding of the tumoral microenvironment is critical to dissect the complexity of cancer, including the reduction in oxygen distribution inside the tumoral mass, defined as tumoral hypoxia. Moreover, hypoxia not only influences the tumoral cells but also the surrounding cells, including those related to the inflammatory processes. In this review, we analyze the participation of HIF, NF-κB, and STAT signaling pathways as the main components that interconnect hypoxia and immune response and how they modulate tumoral growth. In addition, we closely examine the participation of the immune cells and how they are affected by hypoxia, the effects of the progression of cancer, and some innovative applications that take advantage of this knowledge, to suggest potential therapies. Therefore, we contribute to the understanding of the complexity of cancer to propose innovative therapeutic strategies in the future.

Ropivacaine Inhibits Lung Cancer Cell Malignancy Through Downregulation of Cellular Signaling Including HIF-1α In Vitro

Background: Ropivacaine is widely used to induce regional anesthesia during lung cancer surgery. Previous studies reported that amide-linked local anesthetics, e.g., ropivacaine, affected the biological behavior of lung adenocarcinoma cells, but the conclusion is controversial and warrants further study. This study set out to investigate the biological effects of ropivacaine on cultured lung cancer cells and underlying mechanisms.

Methods: Lung cancer cell lines (A549 and H1299) were cultured and then treated with or without ropivacaine (0.5, 1, and 2 mM) for 48 or 72 h. Their proliferation, migration, and invasion together with cell death and molecules including hypoxia inducible factor (HIF)-1α, VEGF, matrix metalloproteinase (MMP)-1, MMP-2, and MMP-9 expression associated with these changes were determined.

Results: Ropivacaine significantly inhibited proliferation and migration, invasion, and cell death in a concentration-dependent manner in both cell lines. Ropivacaine also promoted cell death and induced a concentration- and time-dependent cell arrest towards the G0/G1 phase. Expression of VEGF, MMP-1, MMP-2, MMP-9, and HIF-1α in both cell lines was also inhibited by ropivacaine in a concentration-related manner.

Conclusion: Our data indicated that ropivacaine inhibited lung cancer cell malignancy, which may be associated with downregulation of cell-survival-associated cellular molecules. The translational value of the current work is subjected to further study.

HuR drives lung fibroblast differentiation but not metabolic reprogramming in response to TGF-β and hypoxia

Background

Pulmonary fibrosis is thought to be driven by recurrent alveolar epithelial injury which leads to the differentiation of fibroblasts into α-smooth muscle actin (α-SMA)-expressing myofibroblasts and subsequent deposition of extracellular matrix (ECM). Transforming growth factor beta-1 (TGF-β1) plays a key role in fibroblast differentiation, which we have recently shown involves human antigen R (HuR). HuR is an RNA binding protein that also increases the translation of hypoxia inducible factor (HIF-1α) mRNA, a transcription factor critical for inducing a metabolic shift from oxidative phosphorylation towards glycolysis. This metabolic shift may cause fibroblast differentiation. We hypothesized that under hypoxic conditions, HuR controls myofibroblast differentiation and glycolytic reprogramming in human lung fibroblasts (HLFs).

Methods

Primary HLFs were cultured in the presence (or absence) of TGF-β1 (5 ng/ml) under hypoxic (1% O₂) or normoxic (21% O₂) conditions. Evaluation included mRNA and protein expression of glycolytic and myofibroblast/ECM markers by qRT-PCR and western blot. Metabolic profiling was done by proton nuclear magnetic resonance (¹H- NMR). Separate experiments were conducted to evaluate the effect of HuR on metabolic reprogramming using siRNA-mediated knock-down.

Results

Hypoxia alone had no significant effect on fibroblast differentiation or metabolic reprogramming. While hypoxia- together with TGFβ1- increased mRNA levels of differentiation and glycolysis genes, such as ACTA2, LDHA, and HK2, protein levels of α-SMA and collagen 1 were significantly reduced. Hypoxia induced cytoplasmic translocation of HuR. Knockdown of HuR reduced features of fibroblast differentiation in response to TGF-β1 with and without hypoxia, including α-SMA and the ECM marker collagen I, but had no effect on lactate secretion.

Conclusions

Hypoxia reduced myofibroblasts differentiation and lactate secretion in conjunction with TGF-β. HuR is an important protein in the regulation of myofibroblast differentiation but does not control glycolysis in HLFs in response to hypoxia. More research is needed to understand the functional implications of HuR in IPF pathogenesis.

MicroRNAs and JAK/STAT3 signaling: A new promising therapeutic axis in blood cancers

Blood disorders include a wide spectrum of blood-associated malignancies resulting from inherited or acquired defects. The ineffectiveness of existing therapies against blood disorders arises from different reasons, one of which is drug resistance, so different types of leukemia may show different responses to treatment. Leukemia occurs for a variety of genetic and acquired reasons, leading to uncontrolled proliferation in one or more cell lines. Regarding the genetic defects, oncogene signal transducer and activator of transcription (STAT) family transcription factor, especially STAT3, play an essential role in hematological disorders onset and progress upon mutations, dysfunction, or hyperactivity. Besides, microRNAs, as biological molecules, has been shown to play a dual role in either tumorigenesis and tumor suppression in various cancers. Besides, a strong association between STAT3 and miRNA has been reported. For example, miRNAs can regulate STAT3 via targeting its upstream mediators such as IL6, IL9, and JAKs or directly binding to the STAT3 gene. On the other hand, STAT3 can regulate miRNAs. In this review study, we aimed to determine the role of either microRNAs and STAT3 along with their effect on one another's activity and function in hematological malignancies.

Hypoxia-Induced Photogenic Radicals by Eosin Y for Efficient Phototherapy of Hypoxic Tumors

The current reported photosensitizers generally show a decreased reactive oxygen species (ROS) generation property under hypoxia conditions, which is the main reason for the clinical failure of photodynamic therapy (PDT) in treatment of solid tumors. Herein, for the first time, hypoxia-induced photogenic radicals by eosin Y (Eos) were reported for efficient phototherapy of hypoxic tumors. More importantly, Eos shows a higher ROS and radical production efficiency under hypoxia conditions than under normoxia conditions. The photogenic radicals were captured by electron paramagnetic resonance and further verified by ROS and radical probe. Introducing CoCl₂ as a hypoxia inducer, the photoinduced therapy of the hypoxia cancer cell model and tumor-bearing mice indicated that bovine serum albumin-Eos in hypoxic tumor sites can produce even higher tumor toxicity, thereby crossing the clinical obstacles of hypoxic tumor therapy. This non-oxygen-dependent PDT may open up an avenue for fighting with hypoxia.

Flavagline synthetic derivative induces senescence in glioblastoma cancer cells without being toxic to healthy astrocytes

Glioblastoma (GBM) is one of the most aggressive types of cancer, which begins within the brain. It is the most invasive type of glioma developed from astrocytes. Until today, Temozolomide (TMZ) is the only standard chemotherapy for patients with GBM. Even though chemotherapy extends the survival of patients, there are many undesirable side effects, and most cases show resistance to TMZ. FL3 is a synthetic flavagline which displays potent anticancer activities, and is known to inhibit cell proliferation, by provoking cell cycle arrest, and leads to apoptosis in a lot of cancer cell lines. However, the effect of FL3 in glioblastoma cancer cells has not yet been examined. Hypoxia is a major problem for patients with GBM, resulting in tumor resistance and aggressiveness. In this study, we explore the effect of FL3 in glioblastoma cells under normoxia and hypoxia conditions. Our results clearly indicate that this synthetic flavagline inhibits cell proliferation and induced senescence in glioblastoma cells cultured under both conditions. In addition, FL3 treatment had no effect on human brain astrocytes. These findings support the notion that the FL3 molecule could be used in combination with other chemotherapeutic agents or other therapies in glioblastoma treatments.

CoCl2 simulated hypoxia induce cell proliferation and alter the expression pattern of hypoxia associated genes involved in angiogenesis and apoptosis

BACKGROUND/AIMS

Hypoxia microenvironment plays a crucial role during tumor progression and it tends to exhibit poor prognosis and make resistant to various conventional therapies. HIF-1α acts as an important transcriptional regulator directly or indirectly associated with genes involved in cell proliferation, angiogenesis, apoptosis and energy metabolism during tumor progression in hypoxic microenvironment. This study was aimed to investigate the expression pattern of the hypoxia associated genes and their association during breast cancer progression under hypoxic microenvironment in breast cancer cells.

METHODS

Cell proliferation in MCF-7 and MDA-MB-231 cell lines treated with different concentration of CoCl₂ was analyzed by MTT assay. Flow cytometry was performed to check cell cycle distribution, whereas cell morphology was examined by phase contrast microscopy in both the cells during hypoxia induction. Expression of hypoxia associated genes HIF-1α, VEGF, p53 and BAX were determined by semiquantitative RT-PCR and real-time PCR. Western blotting was performed to detect the expression at protein level.

RESULTS

Our study revealed that cell proliferation in CoCl₂ treated breast cancer cells were concentration dependent and varies with different cell types, further increase in CoCl₂ concentration leads to apoptotic cell death. Further, accumulation of p53 protein in response to hypoxia as compare to normoxia showed that induction of p53 in breast cancer cells is HIF-1α dependent. HIF-1α dependent BAX expression during hypoxia revealed that after certain extent of hypoxia induction, over expression of BAX conquers the effect of anti-apoptotic proteins and ultimately leads to apoptosis in breast cancer cells.

CONCLUSION

In conclusion our results clearly indicate that CoCl₂ simulated hypoxia induce the accumulation of HIF-1α protein and alter the expression of hypoxia associated genes involved in angiogenesis and apoptosis.

Effect of 177Lu-iPSMA on viability and DNA damage of human glioma cells subjected to hypoxia-mimetic conditions

The therapeutic potential of ¹⁷⁷Lu-iPSMA on hypoxic cancer cells has not been yet demonstrated. The aim of this work was to evaluate the radiation dose effect of ¹⁷⁷Lu-iPSMA on viability and DNA damage in U87MG human glioma cells subjected to hypoxia-mimetic conditions. U87MG cells treated with ¹⁷⁷Lu-iPSMA were incubated with CoCl₂ in order to induce hypoxia-mimetic conditions. The cytotoxic and genotoxic effect was evaluated with an in vitro viability test and a neutral comet assay. ¹⁷⁷Lu-iPSMA decreased the cell viability and induced DNA double strand breaks in U87MG human glioma cells under hypoxia-mimetic conditions. ¹⁷⁷Lu-iPSMA produced the maximum effect at 48 h, suggesting that this radiopharmaceutical could be used as a strategy for the treatment of human glioma hypoxic cells.

Acute hypoxic exposure and prolyl-hydroxylase inhibition improves synaptic transmission recovery time from a subsequent hypoxic insult in rat hippocampus

In the CNS short episodes of acute hypoxia can result in a decrease in synaptic transmission which may be fully reversible upon re-oxygenation. Stabilization of hypoxia-inducible factor (HIF) by inhibition of prolyl hydroxylase domain (PHD) enzymes has been shown to regulate the cellular response to hypoxia and confer neuroprotection both in vivo and in vitro. Hypoxic preconditioning has become a novel therapeutic target to induce neuroprotection during hypoxic insults. However, there is little understanding of the effects of repeated hypoxic insults or pharmacological PHD inhibition on synaptic signaling. In this study we have assessed the effects of hypoxic exposure and PHD inhibition on synaptic transmission in the rat CA1 hippocampus. Field excitatory postsynaptic potentials (fEPSPs) were elicited by stimulation of the Schaffer collateral pathway. 30 min hypoxia (gas mixture 95% N₂/5% CO₂) resulted in a significant and fully reversible decrease in fEPSP slope associated with decreases in partial pressures of tissue oxygen. 15-30 min of hypoxia was sufficient to induce stabilization of HIF in hippocampal slices. Exposure to a second hypoxic insult after 60 min resulted in a similar depression of fEPSP slope but with a significantly greater rate of recovery of the fEPSP. Prior single treatment of slices with the PHD inhibitor, dimethyloxalylglycine (DMOG) also resulted in a significantly greater rate of recovery of fEPSP post hypoxia. These results suggest that hypoxia and 'pseudohypoxia' preconditioning may improve the rate of recovery of hippocampal neurons to a subsequent acute hypoxia.

The hypoxia signalling pathway in haematological malignancies

Haematological malignancies are tumours that affect the haematopoietic and the lymphatic systems. Despite the huge efforts to eradicate these tumours, the percentage of patients suffering resistance to therapies and relapse still remains significant. The tumour environment favours drug resistance of cancer cells, and particularly of cancer stem/initiating cells. Hypoxia promotes aggressiveness, metastatic spread and relapse in most of the solid tumours. Furthermore, hypoxia is associated with worse prognosis and resistance to conventional treatments through activation of the hypoxia-inducible factors. Haematological malignancies are not considered solid tumours, and therefore, the role of hypoxia in these diseases was initially presumed to be inconsequential. However, hypoxia is a hallmark of the haematopoietic niche. Here, we will review the current understanding of the role of both hypoxia and hypoxia-inducible factors in different haematological tumours.

The Hypoxia-Mimetic Agent Cobalt Chloride Differently Affects Human Mesenchymal Stem Cells in Their Chondrogenic Potential

Adult stem cells are a promising cell source for cartilage regeneration. They resided in a special microenvironment known as the stem-cell niche, characterized by the presence of low oxygen concentration. Cobalt chloride (CoCl₂) imitates hypoxia in vitro by stabilizing hypoxia-inducible factor-alpha (HIF-1α), which is the master regulator in the cellular adaptive response to hypoxia. In this study, the influence of CoCl₂ on the chondrogenic potential of human MSCs, isolated from dental pulp, umbilical cord, and adipose tissue, was investigated. Cells were treated with concentrations of CoCl₂ ranging from 50 to 400 μM. Cell viability, HIF-1α protein synthesis, and the expression of the chondrogenic markers were analyzed. The results showed that the CoCl₂ supplementation had no effect on cell viability, while the upregulation of chondrogenic markers such as SOX9, COL2A1, VCAN, and ACAN was dependent on the cellular source. This study shows that hypoxia, induced by CoCl₂ treatment, can differently influence the behavior of MSCs, isolated from different sources, in their chondrogenic potential. These findings should be taken into consideration in the treatment of cartilage repair and regeneration based on stem cell therapies.

Cobalt-containing bioactive glasses reduce human mesenchymal stem cell chondrogenic differentiation despite HIF-1α stabilisation

Bioactive glasses (BGs) are excellent delivery systems for the sustained release of therapeutic ions and have been extensively studied in the context of bone tissue engineering. More recently, due to their osteogenic properties and expanding application to soft tissue repair, BGs have been proposed as promising materials for use at the osteochondral interface. Since hypoxia plays a critical role during cartilage formation, we sought to investigate the influence of BGs releasing the hypoxia-mimicking agent cobalt (CoBGs) on human mesenchymal stem cell (hMSC) chondrogenesis, as a novel approach that may guide future osteochondral scaffold design. The CoBG dissolution products significantly increased the level of hypoxia-inducible factor-1 alpha in hMSCs in a cobalt dose-dependent manner. Continued exposure to the cobalt-containing BG extracts significantly reduced hMSC proliferation and metabolic activity, as well as chondrogenic differentiation. Overall, this study demonstrates that prolonged exposure to cobalt warrants careful consideration for cartilage repair applications.

CoCl2 increases the expression of hypoxic markers HIF-1α, VEGF and CXCR4 in breast cancer MCF-7 cells

The aim of the present study was to investigate the effect of a hypoxic environment on the biological behavior of breast cancer MCF-7 cells, using CoCl₂ to mimic the hypoxia model in breast cancer cells. Using 50, 100, 150 and 200 µM CoCl₂ as a hypoxic inducer, a hypoxic model was established in MCF-7 cells in vitro. MTT, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) and western blotting assays were performed to detect MCF-7 cell proliferation under hypoxic conditions and the expression of the hypoxic markers hypoxia-inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and C-X-C motif chemokine receptor 4 (CXCR4) mRNA and that of the associated proteins. The RT-qPCR results revealed that there were no obvious changes in the expression of HIF-1α mRNA; however, the expression of CXCR4 and VEGF mRNA increased significantly following treatment with different CoCl₂ concentrations (P<0.05). The results of western blotting identified that CoCl₂ significantly induced the expression of HIF-1α, CXCR4 and VEGF proteins (P<0.05). The MTT assay revealed that different concentrations of CoCl₂ inhibited the proliferation of MCF-7 cells. The TUNEL assay demonstrated that CoCl₂ was able to trigger apoptosis of MCF-7 cells. Therefore, the results of the present study identified that CoCl₂ is able to control MCF-7 cell proliferation and apoptosis, also increasing the expression of HIF-1α, CXCR4 and VEGF. The present study may aid the discovery of a novel method to prevent cell damage and decrease cell proliferation in order to prevent the occurrence and development of breast cancer.

VHL deficiency augments anthracycline sensitivity of clear cell renal cell carcinomas by down-regulating ALDH2

The von Hippel-Lindau (VHL) is deficient in ∼70% of clear-cell renal cell carcinomas (ccRCC), which contributes to the carcinogenesis and drug resistance of ccRCC. Here we show that VHL-deficient ccRCC cells present enhanced cytotoxicity of anthracyclines in a hypoxia-inducible factor-independent manner. By subtractive proteomic analysis coupling with RNAi or overexpression verification, aldehyde dehydrogenase 2 (ALDH2) is found to be transcriptionally regulated by VHL and contributes to enhanced anthracyclines cytotoxicity in ccRCC cells. Furthermore, VHL regulates ALDH2 expression by directly binding the promoter of -130 bp to -160 bp to activate the transcription of hepatocyte nuclear factor 4 alpha (HNF-4α). In addition, a positive correlation is found among the protein expressions of VHL, HNF-4α and ALDH2 in ccRCC samples. These findings will deepen our understanding of VHL function and shed light on precise treatment for ccRCC patients.

Roles of RUNX in Hypoxia-Induced Responses and Angiogenesis

During the past two decades, Runt domain transcription factors (RUNX1, 2, and 3) have been investigated in regard to their function, structural elements, genetic variants, and roles in normal development and pathological conditions. The Runt family proteins are evolutionarily conserved from Drosophila to mammals, emphasizing their physiological importance. A hypoxic microenvironment caused by insufficient blood supply is frequently observed in developing organs, growing tumors, and tissues that become ischemic due to impairment or blockage of blood vessels. During embryonic development and tumor growth, hypoxia triggers a stress response that overcomes low-oxygen conditions by increasing erythropoiesis and angiogenesis and triggering metabolic changes. This review briefly introduces hypoxic conditions and cellular responses, as well as angiogenesis and its related signaling pathways, and then describes our current knowledge on the functions and molecular mechanisms of Runx family proteins in hypoxic responses, especially in angiogenesis.

TIGAR cooperated with glycolysis to inhibit the apoptosis of leukemia cells and associated with poor prognosis in patients with cytogenetically normal acute myeloid leukemia

Background

Cancer cells show increased glycolysis and take advantage of this metabolic pathway to generate ATP. The TP53-induced glycolysis and apoptosis regulator (TIGAR) inhibits aerobic glycolysis and protects tumor cells from intracellular reactive oxygen species (ROS)-associated apoptosis. However, the function of TIGAR in glycolysis and survival of acute myeloid leukemia cells remains unclear.

Methods

We analyzed TIGAR expression in cytogenetically normal (CN-) AML patients and the correlations with clinical and biological parameters. In vivo and in vitro, we tested whether glycolysis may induce TIGAR expression and evaluated the combination effect of glycolysis inhibitor and TIGAR knockdown on human leukemia cell proliferation.

Results

High TIGAR expression was an independent predictor of poor survival and high incidence of relapse in adult patients with CN-AML. TIGAR also showed high expression in multiple human leukemia cell lines and knockdown of TIGAR activated glycolysis through PFKFB3 upregulation in human leukemia cells. Knockdown of TIGAR inhibited the proliferation of human leukemia cells and sensitized leukemia cells to glycolysis inhibitor both in vitro and in vivo. Furthermore, TIGAR knockdown in combination with glycolysis inhibitor 2-DG led leukemia cells to apoptosis. In addition, the p53 activator Nutlin-3α showed a significant combinational effect with TIGAR knockdown in leukemia cells. However, TIGAR expression and its anti-apoptotic effects were uncoupled from overexpression of exogenous p53 in leukemia cells.

Conclusions

TIGAR might be a predictor of poor survival and high incidence of relapse in AML patients, and the combination of TIGAR inhibitors with anti-glycolytic agents may be novel therapies for the future clinical use in AML patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0360-4) contains supplementary material, which is available to authorized users.

Hypoxia and Hypoxia-Inducible Factors in Leukemias

Despite huge improvements in the treatment of leukemia, the percentage of patients suffering relapse still remains significant. Relapse most often results from a small number of leukemic stem cells (LSCs) within the bone marrow, which are able to self-renew, and therefore reestablish the full tumor. The marrow microenvironment contributes considerably in supporting the protection and development of leukemic cells. LSCs share specific niches with normal hematopoietic stem cells with the niche itself being composed of a variety of cell types, including mesenchymal stem/stromal cells, bone cells, immune cells, neuronal cells, and vascular cells. A hallmark of the hematopoietic niche is low oxygen partial pressure, indeed this hypoxia is necessary for the long-term maintenance of hematopoietic stem/progenitor cells. Hypoxia is a strong signal, principally maintained by members of the hypoxia-inducible factor (HIF) family. In solid tumors, it has been well established that hypoxia triggers intrinsic metabolic changes and microenvironmental modifications, such as the stimulation of angiogenesis, through activation of HIFs. As leukemia is not considered a “solid” tumor, the role of oxygen in the disease was presumed to be inconsequential and remained long overlooked. This view has now been revised since hypoxia has been shown to influence leukemic cell proliferation, differentiation, and resistance to chemotherapy. However, the role of HIF proteins remains controversial with HIFs being considered as either oncogenes or tumor suppressor genes, depending on the study and model. The purpose of this review is to highlight our knowledge of hypoxia and HIFs in leukemic development and therapeutic resistance and to discuss the recent hypoxia-based strategies proposed to eradicate leukemias.

The progress of angiogenic factors in the development of leukemias

Angiogenic factors have been demonstrated to play important roles in modulating angiogenesis of solid tumors. Recently, accumulating studies extensively indicated that some angiogenic factors widely exist in malignant cells of hematologic malignancy, which regulated the expression of a number of genes that were involved in abnormal proliferation, differentiation and apoptosis of these cells. With deep research of angiogenic factors, its expression, function and regulatory mechanism were gradually elucidated, and some of them were related to the development and prognosis of leukemia, or provide more possible strategies for treatment of patients with leukemia. Herein, we summarize the progress in study of some important angiogenic factors and hematological malignancies.

SP1 and USF differentially regulate ADAMTS1 gene expression under normoxic and hypoxic conditions in hepatoma cells

ADAM metallopeptidase with thrombospondin type I motif, 1 (ADAMTS1) that has both antiangiogenic and aggrecanase activity was dysregulated in many pathophysiologic circumstances. However, there is limited information available on the transcriptional regulation of ADAMTS1 gene. Therefore, this study mainly aimed to identify regulatory regions important for the regulation of ADAMTS1 gene under normoxic and hypoxic conditions in human hepatoma cells (HEP3B). Cultured HEP3B cells were exposed to normal oxygen condition, and Cobalt chloride (CoCl2) induced the hypoxic condition, which is an HIF-1 inducer. The cocl2-induced hypoxic condition led to the induced ADAMTS1 mRNA and protein expression in Hepatoma cells. Differential regulation of SP1 and USF transcription factors on ADAMTS1 gene expression was determined by transcriptional activity, mRNA and protein level of ADAMTS1 gene. Ectopic expression of SP1 and USF transcription factors resulted in the decrease in ADAMTS1 transcriptional activity of all promoter constructs consistent with mRNA and protein level in normoxic condition. However, overexpression of SP1 and USF led to the increase of ADAMTS1 gene expressions at mRNA and protein level in hypoxic condition. On the other hand, C/EBPα transcription factor didn't show any statistically significant effect on ADAMTS1 gene expression at mRNA, protein and transcriptional level under normoxic and hypoxic condition.

Hypoxia and free radicals: role in tumor progression and the use of engineering-based platforms to address these relationships

Hypoxia is a feature of all solid tumors, contributing to tumor progression and therapy resistance. Through stabilization of the hypoxia-inducible factor 1 alpha (HIF-1α), hypoxia activates the transcription of a number of genes that sustain tumor progression. Since the seminal discovery of HIF-1α as a hypoxia-responsive master regulator of numerous genes and transcription factors, several groups have reported a novel mechanism whereby hypoxia mediates stabilization of HIF-1α. This process occurs as a result of hypoxia-generated reactive oxygen species (ROS), which, in turn, stabilize the expression of HIF-1α. As a result, a number of genes regulating tumor growth are expressed, fueling ongoing tumor progression. In this review, we outline a role for hypoxia in generating ROS and additionally define the mechanisms contributing to ROS-induced stabilization of HIF-1α.We further explore how ROS-induced HIF-1α stabilization contributes to tumor growth, angiogenesis, metastasis, and therapy response. We discuss a future outlook, describing novel therapeutic approaches for attenuating ROS production while considering how these strategies should be carefully selected when combining with chemotherapeutic agents. As engineering-based approaches have been more frequently utilized to address biological questions, we discuss opportunities whereby engineering techniques may be employed to better understand the physical and biochemical factors controlling ROS expression. It is anticipated that an improved understanding of the mechanisms responsible for the hypoxia/ROS/HIF-1α axis in tumor progression will yield the development of better targeted therapies.

δ-Tocotrienol oxazine derivative antagonizes mammary tumor cell compensatory response to CoCl2-induced hypoxia

In response to low oxygen supply, cancer cells elevate production of HIF-1α, a hypoxia-inducible transcription factor that subsequently acts to stimulate blood vessel formation and promote survival. Studies were conducted to determine the role of δ-tocotrienol and a semisynthetic δ-tocotrienol oxazine derivative, compound 44, on +SA mammary tumor cell hypoxic response. Treatment with 150 µM CoCl₂ induced a hypoxic response in +SA mammary tumor cells as evidenced by a large increase in HIF-1α levels, and combined treatment with compound 44 attenuated this response. CoCl₂-induced hypoxia was also associated with a large increase in Akt/mTOR signaling, activation of downstream targets p70S6K and eIF-4E1, and a significant increase in VEGF production, and combined treatment with compound 44 blocked this response. Additional in vivo studies showed that intralesional treatment with compound 44 in BALB/c mice bearing +SA mammary tumors significantly decreased the levels of HIF-1α, and this effect was associated with a corresponding decrease in Akt/mTOR signaling and activation of downstream targets p70S6kinase and eIF-4E1. These findings demonstrate that treatment with the δ-tocotrienol oxazine derivative, compound 44, significantly attenuates +SA mammary tumor cell compensatory responses to hypoxia and suggests that this compound may provide benefit in the treatment of rapidly growing solid breast tumors.

Downregulation of rRNA transcription triggers cell differentiation

Responding to various stimuli is indispensable for the maintenance of homeostasis. The downregulation of ribosomal RNA (rRNA) transcription is one of the mechanisms involved in the response to stimuli by various cellular processes, such as cell cycle arrest and apoptosis. Cell differentiation is caused by intra- and extracellular stimuli and is associated with the downregulation of rRNA transcription as well as reduced cell growth. The downregulation of rRNA transcription during differentiation is considered to contribute to reduced cell growth. However, the downregulation of rRNA transcription can induce various cellular processes; therefore, it may positively regulate cell differentiation. To test this possibility, we specifically downregulated rRNA transcription using actinomycin D or a siRNA for Pol I-specific transcription factor IA (TIF-IA) in HL-60 and THP-1 cells, both of which have differentiation potential. The inhibition of rRNA transcription induced cell differentiation in both cell lines, which was demonstrated by the expression of the common differentiation marker CD11b. Furthermore, TIF-IA knockdown in an ex vivo culture of mouse hematopoietic stem cells increased the percentage of myeloid cells and reduced the percentage of immature cells. We also evaluated whether differentiation was induced via the inhibition of cell cycle progression because rRNA transcription is tightly coupled to cell growth. We found that cell cycle arrest without affecting rRNA transcription did not induce differentiation. To the best of our knowledge, our results demonstrate the first time that the downregulation of rRNA levels could be a trigger for the induction of differentiation in mammalian cells. Furthermore, this phenomenon was not simply a reflection of cell cycle arrest. Our results provide a novel insight into the relationship between rRNA transcription and cell differentiation.

Opiorphin is a master regulator of the hypoxic response in corporal smooth muscle cells

Men with sickle cell disease (SCD) risk developing priapism. Recognizing that SCD is a disease of hypoxia, we investigated the effect of hypoxia on gene expression in corporal smooth muscle (CSM) cells. Rat CSM cells in vitro were treated with CoCl2 or low oxygen tension to mimic hypoxia. Hypoxic conditions increased expression of genes previously associated with priapism in animal models. Variable coding sequence a1 (Vcsa1; the rat opiorphin homologue, sialorphin), hypoxia-inducible factor 1a (Hif-1a), and A2B adenosine receptor (a2br) were increased by 10-, 4-, and 6-fold, respectively, by treatment with CoCl2, whereas low oxygen tension caused increases in expression of 3-, 4-, and 1.5-fold, respectively. Sialorphin-treated CSM cells increased expression of Hif-1a and a2br by 4-fold, and vcsa1-siRNA treatment reduced expression by ∼50%. Using a Hif-1a inhibitor, we demonstrated up-regulation of a2br by sialorphin is dependent on Hif-1a, and knockdown of vcsa1 expression with vcsa1-siRNA demonstrated that hypoxic-up-regulation of Hif-1a is dependent on vcsa1. In CSM from a SCD mouse, there was 15-fold up-regulation of opiorphin at a life stage prior to priapism. We conclude that in CSM, opiorphins are master regulators of the hypoxic response. Opiorphin up-regulation in response to SCD-associated hypoxia activates CSM "relaxant" pathways; excessive activation of these pathways results in priapism.

Interaction of HIF-1α and Notch3 Is Required for the Expression of Carbonic Anhydrase 9 in Breast Carcinoma Cells

Expression of carbonic anhydrase 9 (CA9) is associated with poor prognosis and increased tumor aggressiveness and does not always correlate with HIF-1α expression. Presently, we analyzed the regulation of CA9 expression during hypoxia by HIF-1α, Notch3, and the von Hippel-Lindau (VHL) in breast carcinoma cells. Both HIF-1α and Notch3 were absolutely required for the expression of CA9 mRNA, protein, and reporter. Reciprocal co-immunoprecipitation of HIF-1α, Notch3 intracellular domain (NICD3), and pVHL demonstrated their association. The presence of common consensus prolyl hydroxylation and pVHL binding motifs (L(XY)LAP);LLPLAP(2191) suggested an oxygen-dependent regulation for NICD3. However, unlike the HIF-1α protein, NICD3 protein levels were not modulated with hypoxia or hypoxia-mimetic agents. Surprisingly, mutations of the common prolyl hydroxylation and pVHL binding domain lead to the loss of CA9 mRNA, protein, and reporter activity. Chromatin immunoprecipitation assay demonstrated the association of NICD3, HIF-1α, and pVHL at the CA9 promoter. Further, the NICD3 mutant defective in prolyl hydroxylation and subsequent pVHL binding caused a reduction in cell proliferation of breast carcinoma cells. We show here for the first time that the interaction of HIF-1α with NICD3 is important for the regulation of CA9 expression. These findings suggest that although CA9 is a hypoxia-responsive gene, its expression is modulated by the interaction of HIF-1α, Notch3, and VHL proteins. Targeting the expression of CA9 by targeting upstream regulators could be useful in cancer/stem cell therapy.

Hypoxia-inducible factor signalling mechanisms in the central nervous system

In the CNS, neurones are highly sensitive to the availability of oxygen. In conditions where oxygen availability is decreased, neuronal function can be altered, leading to injury and cell death. Hypoxia has been implicated in a number of central nervous system pathologies including stroke, head trauma and neurodegenerative diseases. Cellular responses to oxygen deprivation are complex and result in activation of short- and long-term mechanisms to conserve energy and protect cells. Failure of synaptic transmission can be observed within minutes following this hypoxia. The acute effects of hypoxia on synaptic transmission are primarily mediated by altering ion fluxes across membranes, pre-synaptic effects of adenosine and other actions at glutamatergic receptors. A more long-term feature of the response of neurones to hypoxia is the activation of transcription factors such as hypoxia-inducible factor. The activation of hypoxia-inducible factor is governed by a family of dioxygenases called hypoxia-inducible factor prolyl 4 hydroxylases (PHDs). Under hypoxic conditions, PHD activity is inhibited, thereby allowing hypoxia-inducible factor to accumulate and translocate to the nucleus, where it binds to the hypoxia-responsive element sequences of target gene promoters. Inhibition of PHD activity stabilizes hypoxia-inducible factor and other proteins thus acting as a neuroprotective agent. This review will focus on the response of neuronal cells to hypoxia-inducible factor and its targets, including the prolyl hydroxylases. We also present evidence for acute effects of PHD inhibition on synaptic transmission and plasticity in the hippocampus.

What a difference a hydroxyl makes: mutant IDH, (R)-2-hydroxyglutarate, and cancer

Mutations in metabolic enzymes, including isocitrate dehydrogenase 1 (IDH1) and IDH2, in cancer strongly implicate altered metabolism in tumorigenesis. IDH1 and IDH2 catalyze the interconversion of isocitrate and 2-oxoglutarate (2OG). 2OG is a TCA cycle intermediate and an essential cofactor for many enzymes, including JmjC domain-containing histone demethylases, TET 5-methylcytosine hydroxylases, and EglN prolyl-4-hydroxylases. Cancer-associated IDH mutations alter the enzymes such that they reduce 2OG to the structurally similar metabolite (R)-2-hydroxyglutarate [(R)-2HG]. Here we review what is known about the molecular mechanisms of transformation by mutant IDH and discuss their implications for the development of targeted therapies to treat IDH mutant malignancies.

Chloroquine enhances cobalt chloride-induced leukemic cell differentiation via the suppression of autophagy at the late phase

We previously reported that moderate hypoxia and hypoxia-mimetic agents including cobalt chloride (CoCl(2)) induce differentiation of human acute myeloid leukemia (AML) cells through hypoxia-inducible factor-1 α (HIF-1 α), which interacts with and enhances transcriptional activity of CCAAT-enhancer binding factor alpha and Runx1/AML1, two important transcriptional factors for hematopoietic cell differentiation. Here, we show that autophagy inhibitor chloroquine (CQ) increases HIF-1 α accumulation, thus potentiating CoCl(2)-induced growth arrest and differentiation of leukemic cells. Furthermore, the increased effect of CQ on differentiation induction is dependent of the inhibition of autophagosome maturation and degradation, since this sensitization could be mimicked by the suppression of expression of both lysosome-associated membrane proteins 1 and 2 (LAMP1 and LAMP2). These findings not only provide the evidence that CQ is a sensitizer for CoCl(2)-induced differentiation of leukemic cells but also possibly propose the new therapeutic strategy for differentiation induction of AML.

HIF-1α downregulates miR-17/20a directly targeting p21 and STAT3: a role in myeloid leukemic cell differentiation

Hypoxia-inducible factor 1 (HIF-1) is a crucial transcription factor for the cellular adaptive response to hypoxia, which contributes to multiple events in cancer biology. MicroRNAs (miRNAs) are involved in almost all cellular activities such as differentiation, proliferation, and apoptosis. In this work, we use miRNA microarrays to profile miRNA expression in acute myeloid leukemia (AML) cells with inducible HIF-1α expression, and identify 19 differentially expressed miRNAs. Our study shows that HIF-1α represses the expression of miR-17 and miR-20a by downregulating c-Myc expression. These two miRNAs alleviate hypoxia and HIF-1α-induced differentiation of AML cells. More intriguingly, miR-17 and miR-20a directly inhibit the p21 and STAT3 (signal transducer and activator of transcription 3) expression, both of which can reverse miR-17/miR-20a-mediated abrogation of HIF-1α-induced differentiation. Moreover, we show in vivo that miR-20a contributes to HIF-1α-induced differentiation of leukemic cells. Taken together, our results suggest that HIF-1α regulates the miRNA network to interfere with AML cell differentiation, representing a novel molecular mechanism for HIF-1-mediated anti-leukemic action.

Increased expression of heat shock protein 90 under chemical hypoxic conditions protects cardiomyocytes against injury induced by serum and glucose deprivation

Heat shock proteins (HSPs) are critical for adaptation to hypoxia and/or ischemia. Previously, we demonstrated that cobalt chloride (CoCl2), a well-known hypoxia mimetic agent, is an inducer of HSP90. In the present study, we tested the hypothesis that CoCl₂-induced upregulation of HSP90 is able to provide cardioprotection in serum and glucose-deprived H9c2 cardiomyocytes (H9c2 cells). Cell viability was detected using a CCK-8 assay, while HSP90 expression was detected via western blotting. The findings of this study showed that serum and glucose deprivation (SGD) induced significant cytotoxicity, overproduction of reactive oxygen species (ROS) and a loss of mitochondrial membrane potential (MMP) in H9c2 cells. In addition, SGD downregulated the expression of HSP90 in a time-dependent manner. The selective inhibitor of HSP90 17-allylamino-17-demethoxygeldanamycin (17-AAG) aggravated SGD-induced cytotoxicity. CoCl₂ at 100 µM time-dependently enhanced the expression of HSP90. Treatment with CoCl₂ from 50 to 200 µM significantly attenuated cytotoxicity and the downregulation of HSP90 expression induced by SGD for 24 h, respectively. Notably, pretreatment of H9c2 cells with 17-AAG at 2 µM for 60 min before exposure to both CoCl2 (100 µM) and SGD significantly blocked the CoCl2-induced cardioprotective effect, demonstrated by decreased cell viability and MMP loss, as well as increased ROS generation. Taken together, these results suggest that HSP90 may be one of the endogenous defensive mechanisms for resisting ischemia-like injury in H9c2 cells, and that HSP90 plays an important role in chemical hypoxia-induced cardioprotection against SGD-induced injury by its antioxidation and preservation of mitochondrial function.

Cobalt chloride pretreatment promotes cardiac differentiation of human embryonic stem cells under atmospheric oxygen level

Our previous study demonstrated the direct involvement of the HIF-1α subunit in the promotion of cardiac differentiation of murine embryonic stem cells (ESCs). We report the use of cobalt chloride to induce HIF-1α stabilization in human ESCs to promote cardiac differentiation. Treatment of undifferentiated hES2 human ESCs with 50 μM cobalt chloride markedly increased protein levels of the HIF-1α subunit, and was associated with increased expression of early cardiac specific transcription factors and cardiotrophic factors including NK2.5, vascular endothelial growth factor, and cardiotrophin-1. When pretreated cells were subjected to cardiac differentiation, a notable increase in the occurrence of beating embryoid bodies and sarcomeric actinin-positive cells was observed, along with increased expression of the cardiac-specific markers, MHC-A, MHC-B, and MLC2V. Electrophysiological study revealed increased atrial- and nodal-like cells in the cobalt chloride-pretreated group. Confocal calcium imaging analysis indicated that the maximum upstroke and decay velocities were significantly increased in both noncaffeine and caffeine-induced calcium transient in cardiomyocytes derived from the cobalt chloride-pretreated cells, suggesting these cells were functionally more mature. In conclusion, our study demonstrated that cobalt chloride pretreatment of hES2 human ESCs promotes cardiac differentiation and the maturation of calcium homeostasis of cardiomyocytes derived from ESCs.

Hydrogen sulfide protects against chemical hypoxia-induced injury by inhibiting ROS-activated ERK1/2 and p38MAPK signaling pathways in PC12 cells

Hydrogen sulfide (H(2)S) has been proposed as a novel neuromodulator and neuroprotective agent. Cobalt chloride (CoCl(2)) is a well-known hypoxia mimetic agent. We have demonstrated that H(2)S protects against CoCl(2)-induced injuries in PC12 cells. However, whether the members of mitogen-activated protein kinases (MAPK), in particular, extracellular signal-regulated kinase1/2(ERK1/2) and p38MAPK are involved in the neuroprotection of H(2)S against chemical hypoxia-induced injuries of PC12 cells is not understood. We observed that CoCl(2) induced expression of transcriptional factor hypoxia-inducible factor-1 alpha (HIF-1α), decreased cystathionine-β synthase (CBS, a synthase of H(2)S) expression, and increased generation of reactive oxygen species (ROS), leading to injuries of the cells, evidenced by decrease in cell viability, dissipation of mitochondrial membrane potential (MMP) , caspase-3 activation and apoptosis, which were attenuated by pretreatment with NaHS (a donor of H(2)S) or N-acetyl-L cystein (NAC), a ROS scavenger. CoCl(2) rapidly activated ERK1/2, p38MAPK and C-Jun N-terminal kinase (JNK). Inhibition of ERK1/2 or p38MAPK or JNK with kinase inhibitors (U0126 or SB203580 or SP600125, respectively) or genetic silencing of ERK1/2 or p38MAPK by RNAi (Si-ERK1/2 or Si-p38MAPK) significantly prevented CoCl(2)-induced injuries. Pretreatment with NaHS or NAC inhibited not only CoCl(2)-induced ROS production, but also phosphorylation of ERK1/2 and p38MAPK. Thus, we demonstrated that a concurrent activation of ERK1/2, p38MAPK and JNK participates in CoCl(2)-induced injuries and that H(2)S protects PC12 cells against chemical hypoxia-induced injuries by inhibition of ROS-activated ERK1/2 and p38MAPK pathways. Our results suggest that inhibitors of ERK1/2, p38MAPK and JNK or antioxidants may be useful for preventing and treating hypoxia-induced neuronal injury.

Synergistic induction of galectin-1 by CCAAT/enhancer binding protein alpha and hypoxia-inducible factor 1alpha and its role in differentiation of acute myeloid leukemic cells

Galectin-1 is a member of the galectin family and has a high affinity for galactose and N-acetylglucosamine moieties of glycoproteins. It mediates multiple signal transduction pathways to modulate cellular proliferation, survival, differentiation, and migration. However, the mechanisms for the regulation of its expression remain greatly elusive. We reported previously that galectin-1 is a direct target of the hypoxia-inducible factor 1 (HIF-1), a key heterodimeric transcriptional factor for the cellular response to hypoxia. Here we show that CCAAT/enhancer binding protein α (C/EBPα), a critical transcriptional factor for hematopoietic cell differentiation, can directly activate galectin-1 through binding to the -48 to -42 bp region of its promoter. Based on the physical interaction of C/EBPα and HIF-1α, the synergistic transcriptional activity of C/EBPα and HIF-1α on the promoter of the galectin-1 gene is also found by chromatin immunoprecipitation (ChIP), ChIP followed by ChIP (ChIP-reChIP), and luciferase assay. Moreover, knockdown or chemical inhibition of galectin-1 partially blocks the differentiation induced by HIF-1α or C/EBPα, which can be rescued by recombinant galectin-1. These discoveries would shed new insights on the mechanisms for galectin-1 expression regulation and HIF-1α- and C/EBPα-induced leukemic cell differentiation.