HIF1α modulates cell fate reprogramming through early glycolytic shift and upregulation of PDK1-3 and PKM2

Reprogramming somatic cells to a pluripotent state drastically reconfigures the cellular anabolic requirements, thus potentially inducing cancer-like metabolic transformation. Accordingly, we and others previously showed that somatic mitochondria and bioenergetics are extensively remodeled upon derivation of induced pluripotent stem cells (iPSCs), as the cells transit from oxidative to glycolytic metabolism. In the attempt to identify possible regulatory mechanisms underlying this metabolic restructuring, we investigated the contributing role of hypoxia-inducible factor one alpha (HIF1α), a master regulator of energy metabolism, in the induction and maintenance of pluripotency. We discovered that the ablation of HIF1α function in dermal fibroblasts dramatically hampers reprogramming efficiency, while small molecule-based activation of HIF1α significantly improves cell fate conversion. Transcriptional and bioenergetic analysis during reprogramming initiation indicated that the transduction of the four factors is sufficient to upregulate the HIF1α target pyruvate dehydrogenase kinase (PDK) one and set in motion the glycolytic shift. However, additional HIF1α activation appears critical in the early upregulation of other HIF1α-associated metabolic regulators, including PDK3 and pyruvate kinase (PK) isoform M2 (PKM2), resulting in increased glycolysis and enhanced reprogramming. Accordingly, elevated levels of PDK1, PDK3, and PKM2 and reduced PK activity could be observed in iPSCs and human embryonic stem cells in the undifferentiated state. Overall, the findings suggest that the early induction of HIF1α targets may be instrumental in iPSC derivation via the activation of a glycolytic program. These findings implicate the HIF1α pathway as an enabling regulator of cellular reprogramming.

Hypoxia increases gefitinib-resistant lung cancer stem cells through the activation of insulin-like growth factor 1 receptor

Accumulating evidence indicates that a small population of cancer stem cells (CSCs) is involved in intrinsic resistance to cancer treatment. The hypoxic microenvironment is an important stem cell niche that promotes the persistence of CSCs in tumors. Our aim here was to elucidate the role of hypoxia and CSCs in the resistance to gefitinib in non-small cell lung cancer (NSCLC) with activating epidermal growth factor receptor (EGFR) mutation. NSCLC cell lines, PC9 and HCC827, which express the EGFR exon 19 deletion mutations, were exposed to high concentration of gefitinib under normoxic or hypoxic conditions. Seven days after gefitinib exposure, a small fraction of viable cells were detected, and these were referred to as "gefitinib-resistant persisters" (GRPs). CD133, Oct4, Sox2, Nanog, CXCR4, and ALDH1A1-all genes involved in stemness-were highly expressed in GRPs in PC9 and HCC827 cells, and PC9 GRPs exhibited a high potential for tumorigenicity in vivo. The expression of insulin-like growth factor 1 (IGF1) was also upregulated and IGF1 receptor (IGF1R) was activated on GRPs. Importantly, hypoxic exposure significantly increased sphere formation, reflecting the self-renewal capability, and the population of CD133- and Oct4-positive GRPs. Additionally, hypoxia upregulated IGF1 expression through hypoxia-inducible factor 1α (HIF1α), and markedly promoted the activation of IGF1R on GRPs. Knockdown of IGF1 expression significantly reduced phosphorylated IGF1R-expressing GRPs under hypoxic conditions. Finally, inhibition of HIF1α or IGF1R by specific inhibitors significantly decreased the population of CD133- and Oct4-positive GRPs, which were increased by hypoxia in PC9 and HCC827 cells. Collectively, these findings suggest that hypoxia increased the population of lung CSCs resistant to gefitinib in EGFR mutation-positive NSCLC by activating IGF1R. Targeting the IGF1R pathway may be a promising strategy for overcoming gefitinib resistance in EGFR mutation-positive NSCLC induced by lung CSCs and microenvironment factors such as tumor hypoxia.

Targeting the hypoxia-sensing pathway in clinical hematology

Hypoxia-inducible factors (HIFs) are oxygen-sensitive transcription factors regulated by oxygen-dependent prolyl hydroxylase domain (PHD) enzymes and are key to cell adaptation to low oxygen. The hematopoietic stem cell (HSC) niche in the bone marrow is highly heterogeneous in terms of microvasculature and thus oxygen concentration. The importance of hypoxia and HIFs in the hematopoietic environment is becoming increasingly recognized. Many small compounds that inhibit PHDs have been developed, enabling HIFs to be pharmacologically stabilized in an oxygen-independent manner. The use of PHD inhibitors for therapeutic intervention in hematopoiesis is being increasingly investigated. PHD inhibitors are well established to increase erythropoietin production to correct anemia in hemodialysis patients. Pharmacological stabilization of HIF-1α protein with PHD inhibitors is also emerging as an important regulator of HSC proliferation and self-renewal. Administration of PHD inhibitors increases quiescence and decreases proliferation of HSCs in the bone marrow in vivo, thereby protecting them from high doses of irradiation and accelerating hematological recovery. Recent findings also show that stabilization of HIF-1α increases mobilization of HSCs in response to granulocyte colony-stimulating factor and plerixafor, suggesting that PHD inhibitors could be useful agents to increase mobilization success in patients requiring transplantation. These findings highlight the importance of the hypoxia-sensing pathway and HIFs in clinical hematology.

Increased NFAT5 expression stimulates transcription of Hsp70 in preeclamptic placentas

OBJECTIVE

We investigated the expression of heat shock protein 70 (Hsp70), nuclear factor of activated T cells 5 (NFAT5), and hypoxia-induced factor-1α (HIF-1α) in the placentas of normal and preeclamptic pregnancies and in human placental hypoxia models in vitro to examine the regulatory mechanisms of placental Hsp70 expression.

METHODS

The expression levels of HIF-1α, NFAT5, and Hsp70 were examined in placental samples from 10 females with preeclampsia and 10 normotensive control patients and in human choriocarcinoma trophoblast cells treated with 1 mM CoCl2 by western blotting. Using models of placental hypoxia, pharmacological inhibition of HIF-1α with chetomin and shRNA knockdown and overexpression of NFAT5 were performed to investigate the roles of HIF-1α and NFAT5 in induction of Hsp70 by placental hypoxia.

RESULTS

The levels of HIF-1α, NFAT5, and Hsp70 expression were significantly higher in the preeclamptic compared to normal placentas. In the placental hypoxia models, the expression of HIF-1α, NFAT5, and Hsp70 were significantly higher after 3, 6, and 12 h of 1 mM CoCl2 treatment, respectively. Pharmacological inhibition of HIF-1α suppressed the induction of NFAT5 and Hsp70 at the protein level. shRNA knockdown of NFAT5 suppressed the induction of Hsp70 protein and overexpression of NFAT5 stimulated the induction of Hsp70 mRNA and protein in models of human placental hypoxia in vitro.

CONCLUSION

HIF-1α positively regulates the induction of NFAT5 and Hsp70 by placental hypoxia and NFAT5 stimulates transcription of Hsp70 in response to placental hypoxia in models of human placental hypoxia in vitro.

Anti-invasive effects of celastrol in hypoxia-induced fibroblast-like synoviocyte through suppressing of HIF-1α/CXCR4 signaling pathway

Rheumatoid arthritis (RA) joints are in a hypoxic condition. Hypoxia-induced migration and invasion of fibroblast-like synoviocytes (FLSs) are considered to play a critical role in the pathogenesis of RA. Among the key genes upregulated by hypoxia-inducible factor-1α (HIF-1α), CXC chemokine receptor 4 (CXCR4) plays an important role in FLS migration and invasion. Our previous studies have shown that celastrol exerts anti-arthritic effects by inhibiting FLS migration and invasion under normoxic conditions. However, the effect and molecular mechanisms underlying the effect of celastrol on hypoxia-induced FLS migration and invasion are poorly understood. In the present study, we assessed the effect of celastrol on hypoxia-induced FLS migration and invasion. Results showed that celastrol suppressed hypoxia-induced FLS migration and invasion. In addition, we also found that celastrol inhibited hypoxia-induced CXCR4 expression at both the mRNA and the protein levels in RA-FLSs. Meanwhile, it is revealed that celastrol inhibited the transcriptional activity of CXCR4 under hypoxic conditions by suppressing the binding activity of HIF-1α in the CXCR4 promoter, and blocked hypoxia-induced accumulation of nuclear HIF-1α. Furthermore, treatment with HIF-1α inhibitor reduced the hypoxia-induced expression and transcriptional activity of CXCR4. In conclusion, our results indicate that celastrol inhibits hypoxia-induced migration and invasion via suppression of HIF-1α mediated CXCR4 expression in FLSs under hypoxic conditions. These results provide a strong rationale for further testing and validation of the use of celastrol as a new alternative for using in the treatment of RA.

Valproic acid treatment inhibits hypoxia-inducible factor 1α accumulation and protects against burn-induced gut barrier dysfunction in a rodent model

Objective

Burn-induced gut dysfunction plays an important role in the development of sepsis and multiple organ dysfunction. Emerging evidence suggests that hypoxia-inducible factor-1α (HIF-1α) is critical in paracelluar barrier functions via regulating vascular endothelial growth factor (VEGF) and myosin light chain kinase (MLCK) expression. Previous studies have also demonstrated that histone deacetylase inhibitors (HDACIs) can repress HIF-1α. This study aims to examine whether valproic acid (VPA), a HDACI, protects against burn-induced gut barrier dysfunction via repressing HIF-1α-dependent upregulation of VEGF and MLCK expression.

Methods

Rats were subjected to third degree 55% TBSA burns and treated with/ without VPA (300mg/kg). Intestinal barrier dysfunction was evaluated by permeability of intestinal mucosa to fluorescein isothiocyanate (FITC)-dextran and histologic evaluation. Histone acetylation, tight junction protein zonula occludens 1 (ZO-1), VEGF, MLCK and HIF-1α were measured. In addition, CaCO₂ cells were transfected with siRNA directed against HIF-1α and were stimulated with CoCl2 (1mM) for 24 hours with/without VPA (2mM) followed by analysis of HIF-1α, MLCK, VEGF and ZO-1.

Results

Burn insults resulted in a significant increase in intestinal permeability and mucosal damage, accompanied by a significant reduction in histone acetylation, ZO-1, upregulation of VEGF, MLCK expression, and an increase in HIF-1α accumulation. VPA significantly attenuated the increase in intestinal permeability, mucosa damage, histone deacetylation and changes in ZO-1 expression. VPA also attenuated the increased VEGF, MLCK and HIF-1α protein levels. VPA reduced HIF-1α, MLCK and VEGF production and prevented ZO-1 loss in CoCl2-stimulated Caco-2 cells. Moreover, transfection of siRNA directed against HIF-1α led to inhibition of MLCK and VEGF production, accompanied by upregulation of ZO-1.

Conclusions

These results indicate that VPA can protect against burn-induced gut barrier dysfunction. These protective effects may be due to its inhibitory action on HIF-1α, leading to a reduction in intestinal VEGF and MLCK expression and minimizing ZO-1 degradation.

Inhibition of the hypoxia-inducible factor pathway by a G-quadruplex binding small molecule

The hypoxia-inducible transcription factor (HIF) co-ordinates the response of tumours to low oxygen by stimulating genes involved in metabolism and angiogenesis. HIF pathway activation is associated with decreased progression-free survival and increased mortality; compounds that target this pathway are potential agents for the treatment of a range of solid tumour malignancies. Renal cancers are likely to be particularly sensitive to inhibition of the HIF pathway since ~80% show constitutive activation of HIF. We have previously described the di-substituted naphthalene derivative, CL67, which binds to a G-quadruplex higher-order structure in the HIF promoter sequence in vitro. We show here that CL67 blocks HIF expression leading to inhibition of HIF-transactivation and down-regulation of downstream target genes and proteins in renal carcinoma cell lines and in a mouse xenograft model of renal cancer. This inhibition is independent of pathways that control HIF abundance through oxygen-dependant degradation and oxygen dependant HIF sub-unit expression.

[Effect of hypoxia inducible factor-1α on thermotolerance against hyperthemia induced cardiomyocytes apoptosis]

OBJECTIVE

To investigate the expression changes and effects of hypoxia inducible factor-1α (HIF-1α) on non-lethal high temperature induced thermotolerance and its role on thermotolerance protection.

METHODS

H9c2 cardiomyocytes were cultured and pretreated with the HIF-1α inhibitor YC-1, the cells were then subjected to normal temperature (37 °C), thermotolerance induction (40 °C, 3 h), or hyperthermia (43 °C, 2 h). The cells were divided into 8 groups (n = 3 each): normal temperature control group; thermotolerance group; thermotolerance/hyperthermia group; hyperthermia group; DMSO+normal temperature group; YC-1+thermotolerance group; YC-1+thermotolerance/hyperthermia group; YC-1+hyperthermia group. Cell apoptotic rate was assessed by flow cytometry. Western blot was used to detect the expression of HIF-1α and caspase-3.

RESULTS

Flow cytometry results showed that apoptosis rate was similar between control group and thermotolerance group, between DMSO+normal temperature group and YC-1+thermotolerance group, between YC-1+thermotolerance/hyperthermia group and YC-1+hyperthermia group, but was significantly higher in hyperthermia group [(17.35 ± 1.07)%] than in control group [(7.52 ± 1.55)%, P < 0.01] which was partly reduced in thermotolerance/hyperthermia group [(12.58 ± 1.97)%, P < 0.01 vs. thermotolerance group]. Cell apoptosis rate of YC-1+thermotolerance/hyperthermia group (23.75 ± 1.92)% was significantly higher than that of thermotolerance/hyperthermia group [(12.58 ± 1.97)%, P < 0.01], and in YC-1+hyperthermia group [(24.89 ± 1.83)%] than in hyperthermia group [(17.35 ± 1.07)%, P < 0.01]. HIF-1α expression was obviously upregulated in thermotolerance cells compared with control cells, in thermotolerance/hyperthermia cells than in hyperthermia cells, in YC-1+thermotolerance group, YC-1+thermotolerance/hyperthermia group and YC-1+hyperthermia group than in DMSO group (all P < 0.05). Caspase-3 expression was similar between control group and thermotolerance group, but was significantly lower in thermotolerance/hyperthermia group than in hyperthermia group (P < 0.05), significantly higher in YC-1+thermotolerance group, YC-1+thermotolerance/hyperthermia group and YC-1+hyperthermia group than in DMSO group (all P < 0.05) and significantly higher in YC-1+thermotolerance/hyperthermia group than in thermotolerance/hyperthermia group (P < 0.01) and in YC-1+hyperthermia group than in hyperthermia group (P < 0.01).

CONCLUSION

Non-lethal high temperature induced thermotolerance can reduce heat stress-induced cardiomyocytes apoptosis rate via upregulating the expression of HIF-1α and inhibiting caspase-3 signalling pathways.

Melatonin antagonizes hypoxia-mediated glioblastoma cell migration and invasion via inhibition of HIF-1α

Hypoxia is a crucial factor in tumor aggressiveness and resistance to therapy, especially in glioblastoma. Our previous results have shown that melatonin exerts antimigratory and anti-invasive action in glioblastoma cells under normoxia. However, the effect of melatonin on migration and invasion of glioblastoma cells under hypoxic condition remains poorly understood. Here, we show that melatonin strongly reduced hypoxia-mediated invasion and migration of U251 and U87 glioblastoma cells. In addition, we found that melatonin significantly blocked HIF-1α protein expression and suppressed the expression of downstream target genes, matrix metalloproteinase 2 (MMP-2) and vascular endothelial growth factor (VEGF). Furthermore, melatonin destabilized hypoxia-induced HIF-1α protein via its antioxidant activity against ROS produced by glioblastoma cells in response to hypoxia. Along with this, HIF-1α silencing by small interfering RNA markedly inhibited glioblastoma cell migration and invasion, and this appeared to be associated with MMP-2 and VEGF under hypoxia. Taken together, our findings suggest that melatonin suppresses hypoxia-induced glioblastoma cell migration and invasion via inhibition of HIF-1α. Considering the fact that overexpression of the HIF-1α protein is often detected in glioblastoma multiforme, melatonin may prove to be a potent therapeutic agent for this tumor.

Forchlorfenuron disrupts SEPT9_i1 filaments and inhibits HIF-1

Forchlorfenuron (FCF) is a synthetic plant cytokinin that has been shown to alter yeast and mammalian septin organization. Septins are a highly conserved family of GTP-binding cytoskeletal proteins. Mammalian septins are involved in diverse cellular processes including tumorigenesis. We have been studying the interaction between septin 9 isoform 1 (SEPT9_i1) and hypoxia inducible factor-1α (HIF-1α), the oxygen regulated subunit of HIF-1. HIF-1 is a key transcription factor in the hypoxic responses pathway, and its activation has been observed in carcinogenesis and numerous cancers. SEPT9_i1/HIF-1α interaction plays an important role in upregulation of HIF-1 transcriptional activity by preventing HIF-1α's ubiquitination and degradation leading to increased tumor growth and angiogenesis. We tested the hypothesis whether FCF affects SEPT9_i1 filamentous structures and consequently HIF-1 pathway in cancer cells. We showed that FCF suppresses tumorigenic properties, including proliferation, migration and transformation, in prostate cancer cells. FCF did not alter SEPT9_i1 steady state protein expression levels but it affected its filamentous structures and subcellular localization. FCF induced degradation of HIF-1α protein in a dose- and time-dependent manner. This inhibition was also shown in other common cancer types tested. Rapid degradation of HIF-1α protein levels was accompanied by respective inhibition in HIF-1α transcriptional activity. Moreover, HIF-1α protein half-life was markedly decreased in the presence of FCF compared with that in the absence of FCF. The FCF-induced degradation of HIF-1α was mediated in a significant part via the proteasome. To the best of our knowledge, this is the first demonstration of specific manipulation of septin filaments by pharmacological means having downstream inhibitory effects on the HIF-1 pathway.

Lung macrophages contribute to house dust mite driven airway remodeling via HIF-1α

HIF-1α is a transcription factor that is activated during hypoxia and inflammation and is a key regulator of angiogenesis in vivo. During the development of asthma, peribronchial angiogenesis is induced in response to aeroallergens and is thought to be an important feature of sustained chronic allergic inflammation. Recently, elevated HIF-1α levels have been demonstrated in both the lung tissue and bronchoalveolar lavage of allergic patients, respectively. Therefore, we investigated the role of HIF-1α on the development of angiogenesis and inflammation following acute and chronic allergen exposure. Our data shows that intranasal exposure to house dust mite (HDM) increases the expression of HIF-1α in the lung, whilst reducing the expression of the HIF-1α negative regulators, PHD1 and PHD3. Blockade of HIF-1α in vivo, significantly decreased allergic inflammation and eosinophilia induced by allergen, due to a reduction in the levels of IL-5 and Eotaxin-2. Importantly, HIF-1α blockade significantly decreased levels of VEGF-A and CXCL1 in the lungs, which in turn led to a profound decrease in the recruitment of endothelial progenitor cells and a reduction of peribronchial angiogenesis. Furthermore, HDM or IL-4 treatment of primary lung macrophages resulted in significant production of both VEGF-A and CXCL1; inhibition of HIF-1α activity abrogated the production of these factors via an up-regulation of PHD1 and PHD3. These findings suggest that novel strategies to reduce the expression and activation of HIF-1α in lung macrophages may be used to attenuate allergen-induced airway inflammation and angiogenesis through the modulation of VEGF-A and CXCL1 expression.

Clinical Relevance

This study provides new insights into the role of HIF-1α in the development of peribronchial angiogenesis and inflammation in a murine model of allergic airway disease. These findings indicate that strategies to reduce activation of macrophage derived HIF-1α may be used as a target to improve asthma pathology.

Sirtuin-7 inhibits the activity of hypoxia-inducible factors

Hypoxia-inducible factor (HIF) 1 and HIF-2 are heterodimeric proteins composed of an oxygen-regulated HIF-1α or HIF-2α subunit, respectively, and a constitutively expressed HIF-1β subunit, which mediate adaptive transcriptional responses to hypoxia. Here, we report that Sirt7 (sirtuin-7) negatively regulates HIF-1α and HIF-2α protein levels by a mechanism that is independent of prolyl hydroxylation and that does not involve proteasomal or lysosomal degradation. The effect of Sirt7 was maintained in the presence of the sirtuin inhibitor nicotinamide and upon deletion or mutation of its deacetylase domain, indicating a non-catalytic function. Knockdown of Sirt7 led to an increase in HIF-1α and HIF-2α protein levels and an increase in HIF-1 and HIF-2 transcriptional activity. Thus, we identify a novel molecular function of Sirt7 as a negative regulator of HIF signaling.

N-acetylcysteine and allopurinol confer synergy in attenuating myocardial ischemia injury via restoring HIF-1α/HO-1 signaling in diabetic rats

OBJECTIVES

To determine whether or not the antioxidants N-acetylcysteine (NAC) and allopurinol (ALP) confer synergistic cardioprotection against myocardial ischemia/reperfusion (MI/R) injury by stabilizing hypoxia inducible factor 1α (HIF-1α)/heme oxygenase 1 (HO-1) signaling in diabetic myocardium.

METHODS

Control or diabetic [streptozotocin (STZ)-induced] Sprague Dawley rats received vehicle or NAC, ALP or their combination for four weeks starting one week after STZ injection. The animals were then subjected to thirty minutes of coronary artery occlusion followed by two hours reperfusion in the absence or presence of the selective HO-1 inhibitor, tin protoporphyrin-IX (SnPP-IX) or the HIF-1α inhibitor 2-Methoxyestradiol (2ME2). Cardiomyocytes exposed to high glucose were subjected to hypoxia/re-oxygenation in the presence or absence of HIF-1α and HO-1 achieved by gene knock-down with related siRNAs.

RESULTS

Myocardial and plasma levels of 15-F2t-isoprostane, an index of oxidative stress, were significantly increased in diabetic rats while cardiac HO-1 protein and activity were reduced; this was accompanied with reduced cardiac protein levels of HIF-1α, and increased post-ischemic myocardial infarct size and cellular injury. NAC and ALP given alone and in particular their combination normalized cardiac levels of HO-1 and HIF-1α protein expression and prevented the increase in 15-F2t-isoprostane, resulting in significantly attenuated post-ischemic myocardial infarction. NAC and ALP also attenuated high glucose-induced post-hypoxic cardiomyocyte death in vitro. However, all the above protective effects of NAC and ALP were cancelled either by inhibition of HO-1 or HIF-1α with SnPP-IX and 2ME2 in vivo or by HO-1 or HIF-1α gene knock-down in vitro.

CONCLUSION

NAC and ALP confer synergistic cardioprotection in diabetes via restoration of cardiac HIF-1α and HO-1 signaling.

HIF-1α is essential for effective PMN bacterial killing, antimicrobial peptide production and apoptosis in Pseudomonas aeruginosa keratitis

Hypoxia-inducible factor (HIF)-1α, is a transcription factor that controls energy metabolism and angiogenesis under hypoxic conditions, and a potent regulator of innate immunity. The studies described herein examined the role of HIF-1α in disease resolution in BALB/c (resistant, cornea heals) mice after ocular infection with Pseudomonas (P.) aeruginosa. Furthermore, the current studies focused on the neutrophil (PMN), the predominant cell infiltrate in keratitis. Using both siRNA and an antagonist (17-DMAG), the role of HIF-1α was assessed in P. aeruginosa-infected BALB/c mice. Clinical score and slit lamp photography indicated HIF-1α inhibition exacerbated disease and corneal destruction. Real time RT-PCR, immunohistochemistry, ELISA, Greiss and MPO assays, bacterial load, intracellular killing, phagocytosis and apoptosis assays further tested the regulatory role of HIF-1α. Despite increased pro-inflammatory cytokine expression and increased MPO levels after knocking down HIF-1α expression, in vivo studies revealed a decrease in NO production and higher bacterial load. In vitro studies using PMN provided evidence that although inhibition of HIF-1α did not affect phagocytosis, both bacterial killing and apoptosis were significantly affected, as was production of antimicrobial peptides. Overall, data provide evidence that inhibition of HIF-1α converts a normally resistant disease response to susceptible (corneal thinning and perforation) after induction of bacterial keratitis. Although this inhibition does not appear to affect PMN transmigration or phagocytosis, both in vivo and in vitro approaches indicate that the transcriptional factor is essential for effective bacterial killing, apoptosis and antimicrobial peptide production.

Deferoxamine enhances neovascularization and accelerates wound healing in diabetic rats via the accumulation of hypoxia-inducible factor-1α

AIMS

Hypoxia-inducible factor (HIF)-1α plays a pivotal role during the process of wound healing. Previous studies reported that deferoxamine (DFO) could increase HIF-1α stability. This study aimed to investigate the effects of DFO on wound healing in diabetic rats and explore the underlying mechanism both in vivo and in vitro.

METHODS

An excisional diabetic wound model was established and the wound healing among vehicle control, DFO and vascular endothelial growth factor (VEGF) treatment groups was evaluated by macroscopy, histology and Western blot analysis. Human umbilical vein endothelial cells (HUVECs) were treated with DFO or HIF-1α siRNA, and then endothelial tube formation, cell proliferation and migration were examined.

RESULTS

DFO-treated wounds exhibited accelerated wound healing with enhanced granulation formation and increased re-epithelialization. Compared to the vehicle or VEGF treatment, DFO significantly increased neovascularization through up-regulation of HIF-1α and target genes including VEGF and stromal cell-derived factor-1α (SDF-1α). DFO failed to stimulate the expression of VEGF and SDF-1α in HUVECs depleted of HIF-1α. In addition, DFO promoted the angiogenic-associated processes of endothelial tube formation, cell proliferation and migration in HIF-1α dependent manner.

CONCLUSIONS

DFO enhances neovascularization and accelerates diabetic wound healing through the accumulation of HIF-1α and the regulation of endothelial cell function.

Hypoxia-induced cytotoxic drug resistance in osteosarcoma is independent of HIF-1Alpha

Survival rates from childhood cancer have improved dramatically in the last 40 years, such that over 80% of children are now cured. However in certain subgroups, including metastatic osteosarcoma, survival has remained stubbornly poor, despite dose intensive multi-agent chemotherapy regimens, and new therapeutic approaches are needed. Hypoxia is common in adult solid tumours and is associated with treatment resistance and poorer outcome. Hypoxia induces chemotherapy resistance in paediatric tumours including neuroblastoma, rhabdomyosarcoma and Ewing’s sarcoma, in vitro, and this drug resistance is dependent on the oxygen-regulated transcription factor hypoxia inducible factor-1 (HIF-1). In this study the effects of hypoxia on the response of the osteosarcoma cell lines 791T, HOS and U2OS to the clinically relevant cytotoxics cisplatin, doxorubicin and etoposide were evaluated. Significant hypoxia-induced resistance to all three agents was seen in all three cell lines and hypoxia significantly reduced drug-induced apoptosis. Hypoxia also attenuated drug-induced activation of p53 in the p53 wild-type U2OS osteosarcoma cells. Drug resistance was not induced by HIF-1α stabilisation in normoxia by cobalt chloride nor reversed by the suppression of HIF-1α in hypoxia by shRNAi, siRNA, dominant negative HIF or inhibition with the small molecule NSC-134754, strongly suggesting that hypoxia-induced drug resistance in osteosarcoma cells is independent of HIF-1α. Inhibition of the phosphoinositide 3-kinase (PI3K) pathway using the inhibitor PI-103 did not reverse hypoxia-induced drug resistance, suggesting the hypoxic activation of Akt in osteosarcoma cells does not play a significant role in hypoxia-induced drug resistance. Targeting hypoxia is an exciting prospect to improve current anti-cancer therapy and combat drug resistance. Significant hypoxia-induced drug resistance in osteosarcoma cells highlights the potential importance of hypoxia as a target to reverse drug resistance in paediatric osteosarcoma. The novel finding of HIF-1α independent drug resistance suggests however other hypoxia related targets may be more relevant in paediatric osteosarcoma.

Insulin promotes glucose consumption via regulation of miR-99a/mTOR/PKM2 pathway

Insulin is known to regulate multiple cellular functions and is used for the treatment of diabetes. MicroRNAs have been demonstrated to be involved in many human diseases, including Type 2 diabetes. In this study, we showed that insulin decreased miR-99a expression levels, but induced glucose consumption and lactate production, and increased the expression of mTOR, HIF-1α and PKM2 in HepG2 and HL7702 cells. Forced expression of miR-99a or rapamycin treatment blocked insulin-induced PKM2 and HIF-1α expression, and glucose consumption and lactate production. Meanwhile, knockdown of HIF-1α inhibited PKM2 expression and insulin-induced glucose consumption. Taken together, these findings will reveal the role and mechanism of insulin in regulating glycolytic activities via miR-99a/mTOR.

The hypoxia factor Hif-1α controls neural crest chemotaxis and epithelial to mesenchymal transition

One of the most important mechanisms that promotes metastasis is the stabilization of Hif-1 (hypoxia-inducible transcription factor 1). We decided to test whether Hif-1α also was required for early embryonic development. We focused our attention on the development of the neural crest, a highly migratory embryonic cell population whose behavior has been likened to cancer metastasis. Inhibition of Hif-1α by antisense morpholinos in Xenopus laevis or zebrafish embryos led to complete inhibition of neural crest migration. We show that Hif-1α controls the expression of Twist, which in turn represses E-cadherin during epithelial to mesenchymal transition (EMT) of neural crest cells. Thus, Hif-1α allows cells to initiate migration by promoting the release of cell-cell adhesions. Additionally, Hif-1α controls chemotaxis toward the chemokine SDF-1 by regulating expression of its receptor Cxcr4. Our results point to Hif-1α as a novel and key regulator that integrates EMT and chemotaxis during migration of neural crest cells.

Melatonin suppresses tumor progression by reducing angiogenesis stimulated by HIF-1 in a mouse tumor model

The sustained expansion of a tumor mass requires new blood vessel formation to provide rapidly proliferating tumor cells with an adequate supply of oxygen and nutrients. Hypoxia-inducible factor-1 (HIF-1) plays an essential role in tumor angiogenesis and growth by regulating the transcription of genes in response to hypoxic stress. This study was designed to investigate the effects of melatonin on tumor growth and angiogenesis, as well as the mechanism underlying the antitumor activities of melatonin. In this study, we show that the administration of melatonin inhibits tumor growth and blocks tumor angiogenesis in mice. Moreover, melatonin diminished the expression of the HIF-1α protein within the tumor mass during tumorigenesis. Our findings suggest that melatonin is a promising anti-angiogenic therapeutic agent targeting HIF-1α in cancer. Considering that HIF-1α is overexpressed in a majority of human cancers, melatonin could offer a potent therapeutic agent for cancer.

Dissecting fragment-based lead discovery at the von Hippel-Lindau protein:hypoxia inducible factor 1α protein-protein interface

Fragment screening is widely used to identify attractive starting points for drug design. However, its potential and limitations to assess the tractability of often challenging protein:protein interfaces have been underexplored. Here, we address this question by means of a systematic deconstruction of lead-like inhibitors of the pVHL:HIF-1α interaction into their component fragments. Using biophysical techniques commonly employed for screening, we could only detect binding of fragments that violate the Rule of Three, are more complex than those typically screened against classical druggable targets, and occupy two adjacent binding subsites at the interface rather than just one. Analyses based on ligand and group lipophilicity efficiency of anchored fragments were applied to dissect the individual subsites and probe for binding hot spots. The implications of our findings for targeting protein interfaces by fragment-based approaches are discussed.

Hypoxia and hypoxia mimetics decrease aquaporin 5 (AQP5) expression through both hypoxia inducible factor-1α and proteasome-mediated pathways

The alveolar epithelium plays a central role in gas exchange and fluid transport, and is therefore critical for normal lung function. Since the bulk of water flux across this epithelium depends on the membrane water channel Aquaporin 5 (AQP5), we asked whether hypoxia had any effect on AQP5 expression. We show that hypoxia causes a significant (70%) decrease in AQP5 expression in the lungs of mice exposed to hypoxia. Hypoxia and the hypoxia mimetic, cobalt, also caused similar decreases in AQP5 mRNA and protein expression in the mouse lung epithelial cell line MLE-12. The action of hypoxia and cobalt on AQP5 transcription was demonstrated by directly quantifying heternonuclear RNA by real-time PCR. Dominant negative mutants of Hypoxia Inducible Factor (HIF-1α) and HIF-1α siRNA blocked the action of cobalt, showing that HIF-1α is a key component in this mechanism. The proteasome inhibitors, lactacystin or proteasome inhibitor-III completely abolished the effect of hypoxia and cobalt both at the protein and mRNA level indicating that the proteasome pathway is probably involved not only for the stability of HIF-1α protein, but for the stability of unidentified transcription factors that regulate AQP5 transcription. These studies reveal a potentially important physiological mechanism linking hypoxic stress and membrane water channels.

Effects of the silencing of hypoxia-inducible Factor-1 alpha on metastasis of pancreatic cancer

BACKGROUND

Hypoxia plays a crucial role in the development of solid tumors. Hypoxia-inducible factor-1alpha (HIF-1alpha) is essential for this process, and has been suggested to be a target for cancer therapy. New therapeutic approaches for pancreatic cancer are needed owing to the extremely poor prognosis, in large part as a consequence of high rates of metastasis. The mechanism remains to be explored.

AIM

To illustrate the role of hypoxia-inducible factor-1alpha in pancreatic cancer metastasis and the value of the molecule as a target for pancreatic cancer therapy.

MATERIALS AND METHODS

To address this shortcoming, we used both in vitro and in vivo approaches to evaluate the overall effects of HIF-1alpha on pancreatic cancer. We used a plasmid encoding small interfering RNAs (SiRNAs) to silence HIF-1alpha expression in the Panc-1 pancreatic cancer cell line, and used a series of assays to detect changes in gene expression at the protein and mRNA levels, cell proliferation, cell apoptosis, and the abilities of cells to migrate under both hypoxia and normoxia conditions.

RESULTS

Both in vitro and in vivo analysis suggested that hypoxia significantly promotes cell proliferation and migration, resulting in metastasis. Pancreatic cancer cells in which HIF-1alpha expression was inhibited were less invasive, with reduced resistance to hypoxia, impaired migration, and reduced capacity to cause metastasis.

CONCLUSIONS

HIF-1alpha may be a dominant factor driving the metastatic progression of pancreatic cancer and can be a potent therapeutic target for the disease.

PI3 kinase/Akt/HIF-1α pathway is associated with hypoxia-induced epithelial-mesenchymal transition in fibroblast-like synoviocytes of rheumatoid arthritis

Migration and invasion of fibroblast-like synoviocytes (FLSs) are critical in the pathogenesis of rheumatoid arthritis (RA). Hypoxic conditions are present in RA joints, and hypoxia has been extensively studied in angiogenesis and inflammation. However, its effect on the migration and invasion of RA-FLSs remains unknown. In this study, we observed that RA-FLSs exposed to hypoxic conditions experienced epithelial-mesenchymal transition (EMT), with increased cell migration and invasion. We demonstrated that hypoxia-induced EMT was accompanied by increased hypoxia-inducible factor (HIF)-1α expression and activation of Akt. After knockdown or inhibition of HIF-1α in hypoxia by small interfering RNA or genistein (Gen) treatment, the EMT transformation and invasion ability of FLSs were regained. HIF-1α could be blocked by phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, indicating that HIF-1α activation was regulated by the PI3K/Akt pathway. Administration of LY294002 (20 mg/kg, intra-peritoneally) twice weekly and Gen (25 mg/kg, by gavage) daily for 3 weeks from day 20 after primary immunization in a collagen-induced arthritis rat model, markedly alleviated the clinical signs, radiology progression, synovial hyperplasia, and inflammatory cells infiltration of joints. Thus, results of this study suggest that activation of the PI3K/Akt/HIF-1α pathway plays a pivotal role in mediating hypoxia-induced EMT transformation and invasion of RA-FLSs under hypoxia.

Q&A: Celeste Simon on hypoxia-cancer links. Interviewed by Suzanne Rose

M. Celeste Simon, PhD, discusses connections between abnormal hypoxia levels and cancer, as well as her research on hypoxia-inducible factor transcription factors, which mediate responses to hypoxic stress.

Zinc transporter 8 (ZnT8) expression is reduced by ischemic insults: a potential therapeutic target to prevent ischemic retinopathy

The zinc (Zn⁺⁺) transporter ZnT8 plays a crucial role in zinc homeostasis. It’s been reported that an acute decrease in ZnT8 levels impairs β cell function and Zn⁺⁺ homeostasis, which contribute to the pathophysiology of diabetes mellitus (DM). Although ZnT8 expression has been detected in the retinal pigment epithelium (RPE), its expression profile in the retina has yet to be determined. Furthermore, the link between diabetes and ischemic retinopathy is well documented; nevertheless, the molecular mechanism(s) of such link has yet to be defined. Our aims were to; investigate the expression profile of ZnT8 in the retina; address the influence of ischemia on such expression; and evaluate the influence of YC-1; (3-(50-hydroxymethyl-20-furyl)-1-benzyl indazole), a hypoxia inducible factor-1 (HIF-1) inhibitor, on the status of ZnT8 expression. We used real-time RT-PCR, immunohistochemistry, and Western blot in the mouse model of oxygen-induced retinopathy (OIR) and Müller cells to evaluate the effects of ischemia/hypoxia and YC-1 on ZnT8 expression. Our data indicate that ZnT8 was strongly expressed in the outer nuclear layer (ONL), outer plexiform layer (OPL), ganglion cell layer (GCL), and nerve fiber layer (NFL), whereas the photoreceptor layer (PRL), inner nuclear layer (INL) and inner plexiform layer (IPL) showed moderate ZnT8 immunoreactivity. Furthermore, we demonstrate that retinal ischemic insult induces a significant downregulation of ZnT8 at the message and protein levels, YC-1 rescues the injured retina by restoring the ZnT8 to its basal homeostatic levels in the neovascular retinas. Our data indicate that ischemic retinopathy maybe mediated by aberrant Zn⁺⁺ homeostasis caused by ZnT8 downregulation, whereas YC-1 plays a neuroprotective role against ischemic insult. Therefore, targeting ZnT8 provides a therapeutic strategy to combat neovascular eye diseases.