HIF-1alpha expression in response to lipopolysaccaride mediates induction of hepatic inflammatory cytokine TNFalpha

Based on Network Pharmacology and Molecular Docking, the Active Components, Targets, and Mechanisms of Flemingia philippinensis in Improving Inflammation Were Excavated

Flemingia philippinensis, a polyphenol-rich plant, holds potential for improving inflammation, but its mechanisms are not well understood. Therefore, this study employed network pharmacology and molecular docking to explore the mechanism by which Flemingia philippinensis ameliorates inflammation. In this study, 29 kinds of active ingredients were obtained via data mining. Five main active components were screened out for improving inflammation, which were flemichin D, naringenin, chrysophanol, genistein and orobol. In total, 52 core targets were identified, including AKT serine/threonine kinase 1 (AKT1), tumor necrosis factor (TNF), B-cell lymphoma-2 (BCL2), serum albumin (ALB), and estrogen receptor 1 (ESR1). Gene ontology (GO) enrichment analysis identified 2331 entries related to biological processes, 98 entries associated with cellular components, and 203 entries linked to molecular functions. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis yielded 149 pathways, including those involved in EGFR tyrosine kinase inhibitor resistance, endocrine resistance, and the PI3K-Akt signaling pathway. Molecular docking results showed strong binding effects between the main active components and the core targets, with binding energies less than -5 kcal/mol. In summary, this study preliminarily elucidated the underlying mechanisms by which Flemingia philippinensis, through a multi-component, multi-target, and multi-pathway approach, ameliorates inflammation. This provides a theoretical foundation for the subsequent application of Flemingia philippinensis in inflammation amelioration.

Whole transcriptome analysis of RNA expression profiles reveals the potential regulating action of long noncoding RNA in lactating cows fed a high concentrate diet

Subacute ruminal acidosis (SARA) is a common metabolic disease in the dairy farming industry which is usually caused by an excessive amount of high concentrate diet. SARA not only threatens animal welfare but also leads to economic losses in the farming industry. The liver plays an important role in the distribution of nutritional substances and metabolism; however, a high concentrate diet can cause hepatic metabolic disorders and liver injury. Recently, noncoding RNA has been considered as a critical regulator of hepatic disease, however, its role in the bovine liver is limited. In this study, 12 mid-lactating dairy cows were randomly assigned to a control (CON) group (40% concentrate of dry matter, n = 6) and a SARA group (60% concentrate of dry matter, n = 6). After 21 d of treatment, all cows were sacrificed, and liver tissue samples were collected. Three dairy cows were randomly selected from the CON and SARA groups respectively to perform whole transcriptome analysis. More than 20,000 messenger RNA (mRNA), 10,000 long noncoding RNA (lncRNA), 3,500 circular RNA (circRNA) and 1,000 micro RNA (miRNA) were identified. Furthermore, 43 mRNA, 121 lncRNA and 3 miRNA were differentially expressed, whereas no obvious differentially expressed circRNA were detected between the 2 groups. Gene Ontology (GO) annotation revealed that the differentially expressed genes were mainly enriched in oxidoreductase activity, stress, metabolism, the immune response, cell apoptosis, and cell proliferation. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the deferentially expressed genes were highly enriched in the phosphatidylinositol 3 kinase (PI3K)-serine/threonine kinase (AKT) signaling pathway (P < 0.05). According to KEGG pathway analysis, the differentially expressed lncRNA (DElncRNA) target genes were mainly related to proteasomes, peroxisomes, and the hypoxia-inducible factor-1 signaling pathway (P < 0.005). Further bioinformatics and integrative analyses revealed that the lncRNA were strongly correlated with mRNA; therefore, it is reasonable to speculate that lncRNA potentially play important roles in the liver dysfunction induced by SARA. Our study provides a valuable resource for future investigations on the mechanisms of SARA to facilitate an understanding of the importance of lncRNA, and offer functional RNA information.

COX2 Enhances Neovascularization of Inflammatory Tenocytes Through the HIF-1α/VEGFA/PDGFB Pathway

Tendon injuries are among the most challenging in orthopedics. During the early tendon repair, new blood vessel formation is necessary. However, excessive angiogenesis also exacerbates scar formation, leading to pain and dysfunction. A significantly worse outcome was associated with higher expression levels of hypoxia-inducible factor-1 alpha (HIF-1α), and its transcriptional targets vascular endothelial growth factor A (VEGFA) and platelet-derived growth factor B (PDGFB), but the underlying molecular mechanisms remain unclear. In this study, lipopolysaccharide (LPS) was used to induce an inflammatory response in tenocytes. LPS increased the tenocytes' inflammatory factor COX2 expression and activated the HIF-1α/VEGFA/PDGFB pathway. Moreover, the conditioned medium from the tenocytes boosted rat aortic vascular endothelial cell (RAOEC) angiogenesis. Furthermore, Trichostatin A (TSA), an inhibitor of histone deacetylase, was used to treat inflammatory tenocytes. The expression levels of HIF-1α and its transcriptional targets VEGFA and PDGFB decreased, resulting in RAOEC angiogenesis inhibition. Finally, the dual-luciferase reporter gene assay and chromatin immunoprecipitation (ChIP) assay proved that the HIF-1α/PDGFB pathway played a more critical role in tenocyte angiogenesis than the HIF-1α/VEGFA pathway. TSA could alleviate angiogenesis mainly through epigenetic regulation of the HIF-1α/PDGFB pathway. Taken together, TSA might be a promising anti-angiogenesis drug for abnormal angiogenesis, which is induced by tendon injuries.

Hypoxia Exacerbates Inflammatory Acute Lung Injury via the Toll-Like Receptor 4 Signaling Pathway

Acute lung injury (ALI) is characterized by non-cardiogenic diffuse alveolar damage and often leads to a lethal consequence, particularly when hypoxia coexists. The treatment of ALI remains a challenge: pulmonary inflammation and hypoxia both contribute to its onset and progression and no effective prevention approach is available. Here, we aimed to investigate the underlying mechanism of hypoxia interaction with inflammation in ALI and to evaluate hypoxia-inducible factor 1 alpha (HIF-1α)—the crucial modulator in hypoxia—as a potential therapeutic target against ALI. First, we developed a novel ALI rat model induced by a combined low-dose of lipopolysaccharides (LPS) with acute hypoxia. Second, we used gene microarray analysis to evaluate the inflammatory profiles of bronchi alveolar lavage fluid cells of ALI rats. Third, we employed an alveolar macrophage cell line, NR8383 as an in vitro system together with a toll-like receptor 4 (TLR4) antagonist TAK-242, to verify our in vivo findings from ALI animals. Finally, we tested the therapeutic effects of HIF-1α augmentation against inflammation and hypoxia in ALI. We demonstrated that (i) LPS upregulated inflammatory genes, tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6), in the alveolar macrophages of ALI rats, which were further enhanced when ALI combined with hypoxia; (ii) hypoxia exposure could further enhance the upregulation of alveolar macrophageal TLR4 that was noticed in LPS-induced inflammatory ALI, conversely, TLR4 antagonist TAK-242 could suppress the macrophageal expression of TLR4 and inflammatory cytokines, including TNF-α, IL-1β, and IL-6, suggesting that the TLR4 signaling pathway as a central link between inflammation and hypoxia in ALI; (iii) manipulation of HIF-1α in vitro could suppress TLR4 expression induced by combined LPS and hypoxia, via suppressing promoter activity of the TLR4 gene; (iv) preconditioning augmentation of HIF-1α in vivo by HIF hydroxylase inhibitor, DMOG excreted protection against inflammatory, and hypoxic processes in ALI. Together, we see that hypoxia can exacerbate inflammation in ALI via the activation of the TLR4 signaling pathway in alveolar macrophages and predispose impairment of the alveolar-capillary barrier in the development of ALI. Targeting HIF-1α can suppress TLR4 expression and macrophageal inflammation, suggesting the potential therapeutic and preventative value of HIF-1α/TLR4 crosstalk pathway in ALI.

The impact of pretreatment with simvastatin on kidney tissue of rats with acute sepsis

It has been reported that changes in cytokine levels affect mitochondrial functions, levels of hypoxia-inducible factor α (HIF-1α), and tissue damage during sepsis. We aimed to investigate the effects of simvastatin pretreatment on mitochondrial enzyme activities, and on levels of ghrelin, HIF-1α, and thiobarbituric acid reactive substances (TBARS) in kidney tissue during sepsis. Rats were separated into four groups, namely, control, lipopolysaccharides (LPS) (20 mg/kg), simvastatin (20 mg/kg), and simvastatin + LPS. We measured the levels of mitochondrial enzyme activities and TBARS in the kidney using spectrophotometry. The histological structure of the kidney sections was examined after staining with hematoxylin and eosin. Tumor necrosis factor α (TNF-α), IL-10, HIF-1α, and ghrelin immunoreactivity were examined using proper antibodies. In tissue, TNF-α (p < 0.01) and HIF-1α (p < 0.05) levels were increased in the simvastatin + LPS and LPS groups. TBARS levels were higher in the LPS group than in the other groups (p < 0.01), but they were similar in the simvastatin + LPS and control groups (p > 0.05). Ghrelin immunoreactivity was lower in the LPS group (p < 0.05) and higher in the simvastatin + LPS group than in the LPS group (p < 0.01). We observed tubular damage in the sections of the LPS group. There were no differences in mitochondrial enzyme activities between the groups (p > 0.05). We observed that pretreatment of simvastatin caused favorable changes on ghrelin and TBARS levels in rats with sepsis.

Klebsiella pneumoniae Is Able to Trigger Epithelial-Mesenchymal Transition Process in Cultured Airway Epithelial Cells

The ability of some bacterial pathogens to activate Epithelial-Mesenchymal Transition normally is a consequence of the persistence of a local chronic inflammatory response or depends on a direct interaction of the pathogens with the host epithelial cells. In this study we monitored the abilities of the K. pneumoniae to activate the expression of genes related to EMT-like processes and the occurrence of phenotypic changes in airway epithelial cells during the early steps of cell infection. We describe changes in the production of intracellular reactive oxygen species and increased HIF-1α mRNA expression in cells exposed to K. pneumoniae infection. We also describe the upregulation of a set of transcription factors implicated in the EMT processes, such as Twist, Snail and ZEB, indicating that the morphological changes of epithelial cells already appreciable after few hours from the K. pneumoniae infection are tightly regulated by the activation of transcriptional pathways, driving epithelial cells to EMT. These effects appear to be effectively counteracted by resveratrol, an antioxidant that is able to exert a sustained scavenging of the intracellular ROS. This is the first report indicating that strains of K. pneumoniae may promote EMT-like programs through direct interaction with epithelial cells without the involvement of inflammatory cells.

Placental Regulation of Inflammation and Hypoxia after TNF-α Infusion in Mice

PROBLEM

Increased levels of inflammatory cytokines are demonstrated in the serum of women with pre-eclampsia. TNF-α infusion in animal models induces proteinuric hypertension similar to human pre-eclampsia. The effect of TNF-α on regulation of the immune and hypoxic pathways in the developing placenta and their relationship with experimental pre-eclampsia remains unexamined.

METHOD OF STUDY

TNF-α was infused into pregnant mice, and the effects on maternal hypertension, proteinuria, circulating levels of sFlt-1 and corresponding placental changes in molecules responding to inflammation (TLR-3 and TLR-4) and hypoxia (HIF-1α) were examined.

RESULTS

TNF-α infusion resulted in maternal hypertension and proteinuria. Molecular changes in the placenta involved upregulation of TLR-3, TLR-4 and HIF-1α. Serum levels of sFlt-1 were high in pregnant animals, but not further upregulated by TNF-α infusion.

CONCLUSION

A role for maladaptive regulation of TLR and HIF-1α induced by an imbalance in inflammatory cytokines is implicated in the pathogenesis of pre-eclampsia.

Tanshinone IIA therapeutically reduces LPS-induced acute lung injury by inhibiting inflammation and apoptosis in mice

AIM

To study the effects of tanshinone IIA (TIIA) on lipopolysaccharide (LPS)-induced acute lung injury in mice and the underlying mechanisms.

METHODS

Mice were injected with LPS (10 mg/kg, i.p.), then treated with TIIA (10 mg/kg, i.p.). Seven hours after LPS injection, the lungs were collected for histological study. Protein, LDH, TNF-α and IL-1β levels in bronchoalveolar lavage fluid (BALF) and myeloperoxidase (MPO) activity in lungs were measured. Cell apoptosis and Bcl-2, caspase-3, NF-κB and HIF-1α expression in lungs were assayed.

RESULTS

LPS caused marked histological changes in lungs, accompanied by significantly increased lung W/D ratio, protein content and LDH level in BALF, and Evans blue leakage. LPS markedly increased neutrophil infiltration in lungs and inflammatory cytokines in BALF. Furthermore, LPS induced cell apoptosis in lungs, as evidenced by increased TUNEL-positive cells, decreased Bcl-2 content and increased cleaved caspase-3 content. Moreover, LPS significantly increased the expression of NF-κB and HIF-1α in lungs. Treatment of LPS-injected mice with TIIA significantly alleviated these pathological changes in lungs.

CONCLUSION

TIIA alleviates LPS-induced acute lung injury in mice by suppressing inflammatory responses and apoptosis, which is mediated via inhibition of the NF-κB and HIF-1α pathways.

Therapeutic inhibition of prolyl hydroxylase domain-containing enzymes in surgery: putative applications and challenges

Oxygen is essential for metazoans to generate energy. Upon oxygen deprivation adaptive and protective pathways are induced, mediated by hypoxia-inducible factors (HIFs) and prolyl hydroxylase domain-containing enzymes (PHDs). Both play a pivotal role in various conditions associated with prolonged ischemia and inflammation, and are promising targets for therapeutic intervention. This review focuses on aspects of therapeutic PHD modulation in surgically relevant disease conditions such as hepatic and intestinal disorders, wound healing, innate immune responses, and tumorigenesis, and discusses the therapeutic potential and challenges of PHD inhibition in surgical patients.

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

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

B7-1 expression regulates the hypoxia-driven cytoskeleton rearrangement in glomerular podocytes

Chronic hypoxia has been recognized as a common mechanism driving the progression of many glomerular diseases. Glomerular cells, although susceptible to hypoxic injuries, are less studied to unravel the hypoxia-related influences. In the present study, we showed that both lipopolysaccharide (LPS) and hypoxia induced B7-1 and hypoxia-inducible factor (HIF)-1α expression in podocytes. B7-1, an essential player in the regulation of podocyte stress fibers, interacted directly with the NH(2)-terminal oxygenation domain of HIF-1α protein and, therefore, might interfere with the HIF-related oxidative events. The suggestion was supported by the changes in the expression of inducible nitric oxide synthase and nitric oxide. The orderly arranged stress fibers in differentiated podocytes were disrupted by either LPS or hypoxic stimulation, and the disruption could be rescued if they were brought back to normal oxygen tension. Cell motility increased with the stimulation by LPS and hypoxia, most probably mediated by the induction of B7-1 and HIF-1α, respectively. We generated a B7-1 knockdown podocyte cell line using the lentiviral small interfering RNA system. The LPS- and hypoxia-induced stress fiber disruption was largely prevented in the B7-1 knockdown podocytes. The increased cell motility by LPS and hypoxia stimulations was also ameliorated in the B7-knockdown podocytes. In summary, we found that both B7-1 and HIF were upregulated by LPS and hypoxic stimulations in podocytes and they interacted with each other. Hypoxia disrupted the abundant stress fibers and increased cell motility. These hypoxia-induced changes were prevented in B7-knockdown podocytes, and they highlighted the importance of B7-1 expression in the hypoxia-related podocyte injuries.

Molecular oxygen sensing: implications for visceral surgery

BACKGROUND

Since mammalian cells rely on the availability of oxygen, they have devised mechanisms to sense environmental oxygen tension, and to efficiently counteract oxygen deprivation (hypoxia). These adaptive responses to hypoxia are essentially mediated by hypoxia inducible transcription factors (HIFs). Three HIF prolyl hydroxylase enzymes (PHD1, PHD2 and PHD3) function as oxygen sensing enzymes, which regulate the activity of HIFs in normoxic and hypoxic conditions. Many of the compensatory functions exerted by the PHD-HIF system are of immediate surgical relevance since they regulate the biological response of ischemic tissues following ligation of blood vessels, of oxygen-deprived inflamed tissues, and of tumors outgrowing their vascular supply.

PURPOSE

Here, we outline specific functions of PHD enzymes in surgically relevant pathological conditions, and discuss how these functions might be exploited in order to support the treatment of surgically relevant diseases.

Tanshinone IIA-induced attenuation of lung injury in endotoxemic mice is associated with reduction of hypoxia-inducible factor 1α expression

Inhibiting hypoxia-inducible factor (HIF)-1α activity has been proposed as a novel therapeutic target in LPS-induced sepsis syndrome. We have reported that tanshinone IIA (TIIA) can reduce LPS-induced lethality and lung injury in mice, but the precise mechanisms have not been fully described. Therefore, the present study investigated whether the protective effect of TIIA was related to the inhibition of LPS-induced HIF-1α expression and what mechanisms accounted for it. This study showed that TIIA pretreatment improved LPS-induced biochemical and cellular changes and reduced the production of inflammatory cytokines. Pretreatment with TIIA decreased LPS-induced HIF-1α expression in vivo and in vitro. TIIA did not affect the LPS-induced HIF-1α mRNA level but inhibited HIF-1α protein translation by the inhibition of the PI3K/AKT and MAPK pathways and related protein translational regulators, such as p70S6K1, S6 ribosomal protein, 4E-BP1, and eIF4E, and promoted HIF-1α protein degradation via the proteasomal pathway in LPS-stimulated macrophages. These observations partially explain the antiinflammatory effects of TIIA, which provides scientific basis for its application for the treatment of acute lung injury/acute respiratory distress syndrome or sepsis.

Roles of SIRT1 in the acute and restorative phases following induction of inflammation

Endotoxin is a potent inducer of systemic inflammatory responses in human and rodents. Here, we show that in vivo endotoxin triggers a rapid and transient decline in ATP concentration in human peripheral blood leukocytes and murine peripheral blood leukocytes and liver, which is associated with a brief increase in expression of the autophagy indicator LC3-II. In both of these tissues, the ATP concentration reaches a nadir, and autophagy is induced between 2 and 4 h post-endotoxin infusion, and homeostasis is restored within 12 h. Mouse liver SIRT1 and AMP-activated protein kinase (AMPK) protein expression levels decline precipitously within 10 min and remain below detection levels for up to 12 h post-endotoxin administration. In marked contrast, the expression of HIF-1α is induced within 90 min and remains elevated for up to 12 h. The ATP recovery is delayed, and the increases in both HIF-1α expression and autophagy are prolonged in endotoxin-challenged SIRT1 liver knock-out mice. Resveratrol prevents the decline in ATP concentration and SIRT1 expression, as well as the increase in HIF-1α expression and autophagy in liver of endotoxin-challenged wild type mice but not in SIRT1 liver knock-out mice. These results provide novel insight into the state of both cellular bioenergetics and metabolic networks during the acute phase of systemic inflammation and suggest a role for SIRT1 in acute metabolic decline, as well as the restoration of metabolic homeostasis during an inflammatory challenge.

A combination of hypoxia and lipopolysaccharide activates tristetraprolin to destabilize proinflammatory mRNAs such as tumor necrosis factor-alpha

Inflammation is often accompanied by hypoxia because of the high oxygen consumption of invading bacteria and immune cells. During resolution of inflammation, the formation of inflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha), which is produced by macrophages, needs to be terminated. We show in RAW264.7 macrophages that TNF-alpha mRNA as well as intracellular and secreted TNF-alpha protein levels are reduced after prolonged incubations with lipopolysaccharide (LPS) under hypoxic conditions. The decrease in TNF-alpha was mediated by destabilization of TNF-alpha mRNA via a 3'-untranslated region-dependent mechanism. Specifically, the RNA-binding protein tristetraprolin (TTP) increased at mRNA and protein levels after 16-hour incubations with LPS under hypoxia. Interestingly, TTP accumulated in a dephosphorylated and active form, and this accumulation was attributable to reduced p38 mitogen-activated protein kinase activity under these conditions. Knockdown of TTP by small interfering RNA abolished destabilization of TNF-alpha mRNA. Prolonged incubations with LPS under hypoxia also reduced mRNA amounts and stability of other proinflammatory mediators such as macrophage inflammatory protein-2, interleukin-6, and granulocyte macrophage colony-stimulating factor. Therefore, we propose that hypoxia plays a key role during resolution of inflammation by activating posttranscriptional, TTP-dependent regulatory mechanisms.

Transcriptome remodeling in hypoxic inflammation

Hypoxia is an integral component of the inflamed tissue microenvironment. Today, the influence of hypoxia on the natural evolution of inflammatory responses is widely accepted; however, many molecular and cellular mechanisms mediating this relationship remain to be clarified. Hypoxic stress affects several independent transcriptional regulators related to inflammation in which HIF-1 and NF-kappaB play central roles. Transcription factors interact with both HATs and HDACs, which are components of large multiprotein co-regulatory complexes. This review summarizes the current knowledge on hypoxia-responsive transcriptional pathways in inflammation and their importance in the etiology of chronic inflammatory diseases, with the primary focus on transcriptional co-regulators and histone modifications in defining gene-specific transcriptional responses in hypoxia, and on the recent progress in the understanding of hypoxia-mediated epigenetic reprogramming. Furthermore, this review discusses the molecular cross-talk between glucocorticoid anti-inflammatory pathways and hypoxia.

Organ preservation solutions attenuate accumulation and nuclear translocation of hypoxia-inducible factor-1alpha in the hepatoma cell line HepG2

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a key transcription factor orchestrating hypoxic and inflammatory reactions. Here, we determined the impact of organ preservation solutions (Celsior; histidine-tryptophan-ketoglutarate solution, HTK; University of Wisconsin solution; UW), oxygen supply, and temperature on HIF-1alpha accumulation, recorded by Western blotting and immunocytochemistry, in the human hepatoma cell line HepG2. Generation of reactive oxygen species (ROS), NO, and cell viability were concomitantly assessed. At 4 degrees C, HIF-1alpha accumulation was not detectable. In normothermic (37 degrees C) cell culture medium (Dulbecco's Modified Eagle's Medium, DMEM), HepG2 cells accumulated HIF-1alpha even in normoxia (21% O(2)) which was not observed in either of the preservation solutions. This correlated to high generation of NO, a normoxic stabilizer of HIF-1alpha, and L-arginine content (substrate for NO synthesis) in DMEM, and low NO production and absence of L-arginine in preservation solutions. In normothermic hypoxia up to 24 h, intracellular HIF-1alpha accumulated in all conditions, but less in preservation solutions compared to DMEM. The inhibitory effect on accumulation and nuclear translocation was most prominent for HTK, the only solution containing the activator of HIF-1alpha degradation, alpha-ketoglutarate. Addition of other intermediates of the tricarbon acid cycle-succinate, fumarate, malate-did not alter HIF-1alpha accumulation, although succinate exhibited a beneficial effect on cell viability in cold storage. In conclusion, preservation solutions attenuate accumulation and nuclear translocation of the transcription factor HIF-1alpha, and this property is seemingly related to their chemical composition (L-arginine, alpha-ketoglutarate). Thus, it appears feasible to design preservation solution specifically to modify HIF-1alpha accumulation and nuclear translocation.

HIF-1alpha mediates the induction of IL-8 and VEGF expression on infection with Afa/Dr diffusely adhering E. coli and promotes EMT-like behaviour

Microbes regulate a large panel of intracellular signalling events that can promote inflammation and/or enhance tumour progression. Indeed, it has been shown that infection of human intestinal cells with the Afa/Dr diffusely adhering E. coli C1845 strain induces expression of pro-angiogenic and pro-inflammatory genes. Here, we demonstrate that exposure of cryptic-like intestinal epithelial cells to C1845 bacteria induces HIF-1alpha protein levels. This effect depends on the binding of F1845 adhesin to the membrane-associated DAF receptor that initiates signalling cascades promoting translational mechanisms. Indeed, inhibition of MAPK and PI-3K decreases HIF-1alpha protein levels and blocks C1845-induced phosphorylation of the ribosomal S6 protein. Using RNA interference we show that bacteria-induced HIF-1alpha regulates the expression of IL-8, VEGF and Twist1, thereby pointing to a role for HIF-1 in angiogenesis and inflammation. In addition, infection correlates with a loss of E-cadherin and cytokeratin 18 and a rise in fibronectin, suggesting that bacteria may induce an epithelial to mesenchymal transition-like phenotype. Since HIF-1alpha silencing results in reversion of bacteria-induced EMT markers, we speculate that HIF-1alpha plays a key role linking bacterial infection to angiogenesis, inflammation and some aspects of cancer initiation.

Reactive oxygen species-generating mitochondrial DNA mutation up-regulates hypoxia-inducible factor-1alpha gene transcription via phosphatidylinositol 3-kinase-Akt/protein kinase C/histone deacetylase pathway

Lewis lung carcinoma-derived high metastatic A11 cells constitutively overexpress hypoxia-inducible factor (HIF)-1alpha mRNA compared with low metastatic P29 cells. Because A11 cells exclusively possess a G13997A mutation in the mitochondrial NADH dehydrogenase subunit 6 (ND6) gene, we addressed here a causal relationship between the ND6 mutation and the activation of HIF-1alpha transcription, and we investigated the potential mechanism. Using trans-mitochondrial cybrids between A11 and P29 cells, we found that the ND6 mutation was directly involved in HIF-1alpha mRNA overexpression. Stimulation of HIF-1alpha transcription by the ND6 mutation was mediated by overproduction of reactive oxygen species (ROS) and subsequent activation of phosphatidylinositol 3-kinase (PI3K)-Akt and protein kinase C (PKC) signaling pathways. The up-regulation of HIF-1alpha transcription was abolished by mithramycin A, an Sp1 inhibitor, but luciferase reporter and chromatin immunoprecipitation assays indicated that Sp1 was necessary but not sufficient for HIF-1alpha mRNA overexpression in A11 cells. On the other hand, trichostatin A, a histone deacetylase (HDAC) inhibitor, markedly suppressed HIF-1alpha transcription in A11 cells. In accordance with this, HDAC activity was high in A11 cells but low in P29 cells and in A11 cells treated with the ROS scavenger ebselene, the PI3K inhibitor LY294002, and the PKC inhibitor Ro31-8220. These results suggest that the ROS-generating ND6 mutation increases HIF-1alpha transcription via the PI3K-Akt/PKC/HDAC pathway, leading to HIF-1alpha protein accumulation in hypoxic tumor cells.

[Mitochondrial dysfunction during sepsis, impact and possible regulating role of hypoxia-inducible factor-1alpha]

There is a direct correlation between the development of the multiple organ dysfunction syndrome (MODS) and the elevated mortality associated with sepsis. The mechanisms responsible for MODS development are being studied, however, the main efforts regarding MODS evaluation have focused on oxygen delivery optimization and on the modulation of the characteristic inflammatory cascade of sepsis, all with negative results. Recent studies have shown that there is development of tissue acidosis, even when there are normal oxygen conditions and limited presence of tissue cellular necrosis or apoptosis, which would indicate that cellular energetic dysfunction may be a central element in MODS pathogenesis. Mitochondrias are the main source of cellular energy, central regulators of cell death and the main source for reactive oxygen species. Several mechanisms contribute to mitochondrial dysfunction during sepsis, that is blockage of pyruvate entry into the Krebs cycle, oxidative phosphorylation substrate use in other enzymatic complexes, enzymatic complex inhibition and membrane damage mediated by oxidative stress, and reduction in mitochondrial content. Hypoxia-inducible factor-1alpha (HIF-1alpha) is a nuclear transcription factor with a central role in the regulation of cellular oxygen homeostasis. Its induction under hypoxic conditions is associated to the expression of hundreds of genes that coordinate the optimization of cellular oxygen delivery and the cellular energy metabolism. HIF-1alpha can also be stabilized under normoxic condition during inflammation and this activation seems to be associated with a prominent pro-inflammatory profile, with lymphocytes dysfunction, and to a reduction in cellular oxygen consumption. Further studies should establish a role for HIF-1alpha as a therapeutic target.

HIF-1alpha-dependent gene expression program during the nucleic acid-triggered antiviral innate immune responses

Recent studies suggest a novel role of HIF-1alpha under non-hypoxic conditions, including antibacterial and antiviral innate immune responses. However, the identity of the pathogen-associated molecular pattern which triggers HIF-1alpha activation during the antiviral response remains to be identified. Here, we demonstrate that cellular administration of double-stranded nucleic acids, the molecular mimics of viral genomes, results in the induction of HIF-1alpha protein level as well as the increase in HIF-1alpha target gene expression. Whole-genome DNA microarray analysis revealed that double-stranded nucleic acid treatment triggers induction of a number of hypoxia-inducible genes, and induction of these genes are compromised upon siRNA-mediated HIF-1alpha knock-down. Interestingly, HIF-1alpha knock-down also resulted in down-regulation of a number of genes involved in antiviral innate immune responses. Our study demonstrates that HIF-1alpha activation upon nucleic acid-triggered antiviral innate immune responses plays an important role in regulation of genes involved in not only hypoxic response, but also immune response.

Inhibition of oxygen sensors as a therapeutic strategy for ischaemic and inflammatory disease

Cells in the human body need oxygen to function and survive, and severe deprivation of oxygen, as occurs in ischaemic heart disease and stroke, is a major cause of mortality. Nevertheless, other organisms, such as the fossorial mole rat or diving seals, have acquired the ability to survive in conditions of limited oxygen supply. Hypoxia tolerance also allows the heart to survive chronic oxygen shortage, and ischaemic preconditioning protects tissues against lethal hypoxia. The recent discovery of a new family of oxygen sensors--including prolyl hydroxylase domain-containing proteins 1-3 (PHD1-3)--has yielded exciting novel insights into how cells sense oxygen and keep oxygen supply and consumption in balance. Advances in understanding of the role of these oxygen sensors in hypoxia tolerance, ischaemic preconditioning and inflammation are creating new opportunities for pharmacological interventions for ischaemic and inflammatory diseases.

Nickel and the microbial toxin, MALP-2, stimulate proangiogenic mediators from human lung fibroblasts via a HIF-1alpha and COX-2-mediated pathway

Hypoxia-inducible factor (HIF-1alpha) and cyclooxygenase-2 (COX-2) have been implicated in the regulation of inflammatory-like processes that lead to angiogenesis and fibrotic disorders. Here we demonstrate that in human lung fibroblasts (HLFs) treated with mixed exposures to chemical and microbial stimuli, HIF-1alpha stabilization plays a pivotal role in the induction of COX-2 mRNA and protein, driving the release of vascular endothelial growth factor (VEGF) and proangiogenic and profibrotic chemokines. Upon costimulation with Ni and the mycoplasma-derived lipopeptide macrophage-activating lipopeptide-2 (MALP-2), there was a synergistic induction of CXCL1 and CXCL5 mRNA and protein release from HLF, as well as an enhanced response in VEGF compared to either stimulus alone. Consistent with our previous findings that Ni and MALP-2 stimulates the induction of CXCL8 via a COX-2-mediated pathway, CXCL1, CXCL5, and VEGF release were also regulated by COX-2. Ni induced the stabilization of HIF-1alpha protein in HLF, which was further enhanced in the presence of MALP-2. Depletion of HIF-1alpha using siRNA blocked COX-2 induction by Ni and MALP-2 along with the release of VEGF, CXCL1, CXCL5, and CXCL8. Our results indicate that Ni and MALP-2 interact to promote an angiogenic profibrotic phenotype in HLF. Moreover, these findings reveal a potential role for HIF-1alpha in mediating chemical-induced alterations in cellular response to microbial stimuli, modulating pulmonary inflammation and its consequences such as fibrosis and angiogenesis.

Regulation of gene expression by hypoxia

Hypoxia induces profound changes in the cellular gene expression profile. The discovery of a major transcription factor family activated by hypoxia, HIF (hypoxia-inducible factor), and the factors that contribute to HIF regulation have greatly enhanced our knowledge of the molecular aspects of the hypoxic response. However, in addition to HIF, other transcription factors and cellular pathways are activated by exposure to reduced oxygen. In the present review, we summarize the current knowledge of how additional hypoxia-responsive transcription factors integrate with HIF and how other cellular pathways such as chromatin remodelling, translation regulation and microRNA induction, contribute to the co-ordinated cellular response observed following hypoxic stress.

Lipopolysaccharide induces hypoxia-inducible factor-1 alpha mRNA expression and activation via NADPH oxidase and Sp1-dependent pathway in BV2 murine microglial cells

Hypoxia-inducible factor-1 (HIF-1), the key transcription factor of hypoxia-inducible genes, is known to be involved in inflammation and immune response, but little is known about the regulation of HIF-1 during microglial activation. Thus, we examined effect of lipopolysaccharide (LPS) on HIF-1 activation and its signaling mechanism in BV2 microglial cells. LPS induced HIF-1alpha mRNA and protein expression as well as HIF-1 transcriptional activation. Moreover, HIF-1alpha knockdown by small interfering RNA (siRNA) decreased LPS-induced expression of hypoxia responsive genes, VEGF, iNOS, and COX-2. We then showed that LPS-induced HIF-1alpha mRNA expression was blocked by an antioxidant, NADPH oxidase inhibitors, and siRNA of gp91phox, a subunit of NADPH oxidase. In addition, we showed that specific pharmacological inhibitors of PI 3-kinase and protein kinase C decreased LPS-induced HIF-1alpha mRNA expression. Finally, we showed that inhibition of transcription factor Sp1 by mithramycin A or Sp1 siRNA decreased LPS-induced HIF-1alpha mRNA and protein expression. Consistently, LPS increased Sp1 DNA binding and its transcriptional activity. Taken together, these results suggest that LPS induces HIF-1alpha mRNA expression and activation via NADPH oxidase and Sp1 in BV2 microglia.