Now showing 1 - 10 of 11
  • Publication
    REST mediates resolution of HIF-dependent gene expression in prolonged hypoxia
    The hypoxia-inducible factor (HIF) is a key regulator of the cellular response to hypoxia which promotes oxygen delivery and metabolic adaptation to oxygen deprivation. However, the degree and duration of HIF-1a expression in hypoxia must be carefully balanced within cells in order to avoid unwanted side effects associated with excessive activity. The expression of HIF-1a mRNA is suppressed in prolonged hypoxia, suggesting that the control of HIF1A gene transcription is tightly regulated by negative feedback mechanisms. Little is known about the resolution of the HIF-1a protein response and the suppression of HIF-1a mRNA in prolonged hypoxia. Here, we demonstrate that the Repressor Element 1-Silencing Transcription factor (REST) binds to the HIF-1a promoter in a hypoxia-dependent manner. Knockdown of REST using RNAi increases the expression of HIF-1a mRNA, protein and transcriptional activity. Furthermore REST knockdown increases glucose consumption and lactate production in a HIF-1a- (but not HIF-2a-) dependent manner. Finally, REST promotes the resolution of HIF-1a protein expression in prolonged hypoxia. In conclusion, we hypothesize that REST represses transcription of HIF-1a in prolonged hypoxia, thus contributing to the resolution of the HIF-1a response.
      287Scopus© Citations 54
  • Publication
    FIH Regulates Cellular Metabolism through Hydroxylation of the Deubiquitinase OTUB1
    The asparagine hydroxylase, factor inhibiting HIF (FIH), confers oxygen-dependence upon the hypoxia-inducible factor (HIF), a master regulator of the cellular adaptive response to hypoxia. Studies investigating whether asparagine hydroxylation is a general regulatory oxygen-dependent modification have identified multiple non-HIF targets for FIH. However, the functional consequences of this outside of the HIF pathway remain unclear. Here, we demonstrate that the deubiquitinase ovarian tumor domain containing ubiquitin aldehyde binding protein 1 (OTUB1) is a substrate for hydroxylation by FIH on N22. Mutation of N22 leads to a profound change in the interaction of OTUB1 with proteins important in cellular metabolism. Furthermore, in cultured cells, overexpression of N22A mutant OTUB1 impairs cellular metabolic processes when compared to wild type. Based on these data, we hypothesize that OTUB1 is a target for functional hydroxylation by FIH. Additionally, we propose that our results provide new insight into the regulation of cellular energy metabolism during hypoxic stress and the potential for targeting hydroxylases for therapeutic benefit.
      302Scopus© Citations 75
  • Publication
    Carbon dioxide-sensing in organisms and its implications for human disease
    The capacity of organisms to sense changes in the levels of internal and external gases and to respond accordingly is central to a range of physiologic and pathophysiologic processes. Carbon dioxide, a primary product of oxidative metabolism is one such gas that can be sensed by both prokaryotic and eukaryotic cells and in response to altered levels, elicit the activation of multiple adaptive pathways. The outcomes of activating CO2-sensitive pathways in various species include increased virulence of fungal and bacterial pathogens, prey-seeking behavior in insects as well as taste perception, lung function, and the control of immunity in mammals. In this review, we discuss what is known about the mechanisms underpinning CO2 sensing across a range of species and consider the implications of this for physiology, disease progression, and the possibility of developing new therapeutics for inflammatory and infectious disease.
      544Scopus© Citations 103
  • Publication
    Hypoxia-dependent regulation of inflammatory pathways in immune cells
    (American Society for Clinical Investigation, 2016-07-25) ; ; ;
    Uncontrolled inflammation underpins a diverse range of diseases where effective therapy remains an unmet clinical need. Hypoxia is a prominent feature of the inflammatory microenvironment that regulates key transcription factors including HIF and NF-κB in both innate and adaptive immune cells. In turn, altered activity of the pathways controlled by these factors can affect the course of inflammation through the regulation of immune cell development and function. In this review, we will discuss these pathways and the oxygen sensors that confer hypoxic sensitivity in immune cells. Furthermore, we will describe how hypoxia-dependent pathways contribute to immunity and discuss their potential as therapeutic targets in inflammatory and infectious disease.
      459Scopus© Citations 148
  • Publication
    Regulation of gene expression by carbon dioxide
    (Wiley Blackwell (Blackwell Publishing -The Physiological Society), 2011-01-04) ;
    Carbon dioxide (CO2) is a physiological gas found at low levels in the atmosphere and produced in cells during the process of aerobic respiration. Consequently, the levels of CO2 within tissues are usually significantly higher than those found externally. Shifts in tissue levels of CO2 (leading to either hypercapnia or hypocapnia) are associated with a number of pathophysiological conditions in humans and can occur naturally in niche habitats such as those of burrowing animals. Clinical studies have indicated that such altered CO2 levels can impact upon disease progression. Recent advances in our understanding of the biology of CO2 has shown that like other physiological gases such as molecular oxygen (O2) and nitric oxide (NO), CO2 levels can be sensed by cells resulting in the initiation of physiological and pathophysiological responses. Acute CO2 sensing in neurons and peripheral and central chemoreceptors is important in rapidly activated responses including olfactory signalling, taste sensation and cardiorespiratory control. Furthermore, a role for CO2 in the regulation of gene transcription has recently been identified with exposure of cells and model organisms to high CO2 leading to suppression of genes involved in the regulation of innate immunity and inflammation. This latter, transcriptional regulatory role for CO2, has been largely attributed to altered activity of the NF-κB family of transcription factors. Here, we review our evolving understanding of how CO2 impacts upon gene transcription.
    Scopus© Citations 35  380
  • Publication
    The role of HIF in immunity and inflammation
    Uncontrolled or non-resolving inflammation underpins a range of disease states including rheumatoid arthritis, inflammatory bowel disease and atherosclerosis. Hypoxia is a prominent feature of chronically inflamed tissues. This is due to elevated oxygen consumption by highly metabolically active inflamed resident cells and activated infiltrating immunocytes, as well as diminished oxygen supply due to vascular dysfunction. Tissue hypoxia can have a significant impact upon inflammatory signaling pathways in immune and non-immune cells and this can impact upon disease progression. In this review, we will discuss the relationship between tissue hypoxia and inflammation and identify how hypoxia-sensitive signaling pathways are potential therapeutic targets in chronic inflammatory disease.
      1317Scopus© Citations 122
  • Publication
    Loss of Prolyl Hydroxylase-1 Protects Against Colitis Through Reduced Epithelial Cell Apoptosis and Increased Barrier Function
    Background & Aims: Hypoxia inducible factor (HIF) prolyl hydroxylase inhibitors are protective in mouse models of inflammatory bowel disease (IBD). Here, we investigated the therapeutic target(s) and mechanism(s) involved. Methods: The effect of genetic deletion of individual HIF-prolyl hydroxylase (PHD) enzymes on the development of dextran sulphate sodium (DSS)–induced colitis was examined in mice. Results: PHD1−/−, but not PHD2+/− or PHD3−/−, mice were less susceptible to the development of colitis than wild-type controls as determined by weight loss, disease activity, colon histology, neutrophil infiltration, and cytokine expression. Reduced susceptibility of PHD1−/− mice to colitis was associated with increased density of colonic epithelial cells relative to wild-type controls, which was because of decreased levels of apoptosis that resulted in enhanced epithelial barrier function. Furthermore, with the use of cultured epithelial cells it was confirmed that hydroxylase inhibition reversed DSS-induced apo tosis and barrier dysfunction. Finally, PHD1 levels were increased with disease severity in intestinal tissue from patients with IBD and in colonic tissues from DSS-treated mice. Conclusions: These results imply a role for PHD1 as a positive regulator of intestinal epithelial cell apoptosis in the inflamed colon. Genetic loss of PHD1 is protective against colitis through decreased epithelial cell apoptosis and consequent enhancement of intestinal epithelial barrier function. Thus, targeted PHD1 inhibition may represent a new therapeutic approach in IBD.
      576Scopus© Citations 170
  • Publication
    Hypercapnia Suppresses the HIF-dependent Adaptive Response to Hypoxia
    Molecular oxygen and carbon dioxide are the primary gaseous substrate and product of oxidative metabolism, respectively. Hypoxia (low oxygen) and hypercapnia (high carbon dioxide) are co-incidental features of the tissue microenvironment in a range of pathophysiologic states, including acute and chronic respiratory diseases. The hypoxia-inducible factor (HIF) is the master regulator of the transcriptional response to hypoxia; however, little is known about the impact of hypercapnia on gene transcription. Because of the relationship between hypoxia and hypercapnia, we investigated the effect of hypercapnia on the HIF pathway. Hypercapnia suppressed HIF-α protein stability and HIF target gene expression both in mice and cultured cells in a manner that was at least in part independent of the canonical O2-dependent HIF degradation pathway. The suppressive effects of hypercapnia on HIF-α protein stability could be mimicked by reducing intracellular pH at a constant level of partial pressure of CO2 Bafilomycin A1, a specific inhibitor of vacuolar-type H(+)-ATPase that blocks lysosomal degradation, prevented the hypercapnic suppression of HIF-α protein. Based on these results, we hypothesize that hypercapnia counter-regulates activation of the HIF pathway by reducing intracellular pH and promoting lysosomal degradation of HIF-α subunits. Therefore, hypercapnia may play a key role in the pathophysiology of diseases where HIF is implicated.
      97Scopus© Citations 48
  • Publication
    Regulation of IL-1β-induced NF-κB by hydroxylases links key hypoxic and inflammatory signaling pathways
    Hypoxia is a prominent feature of chronically inflamed tissues. Oxygen-sensing hydroxylases control transcriptional adaptation to hypoxia through the regulation of hypoxia-inducible factor (HIF) and nuclear factor κB (NF-κB), both of which can regulate the inflammatory response. Furthermore, pharmacologic hydroxylase inhibitors reduce inflammation in multiple animal models. However, the underlying mechanism(s) linking hydroxylase activity to inflammatory signaling remains unclear. IL-1β, a major proinflammatory cytokine that regulates NF-κB, is associated with multiple inflammatory pathologies. We demonstrate that a combination of prolyl hydroxylase 1 and factor inhibiting HIF hydroxylase isoforms regulates IL-1β-induced NF-κB at the level of (or downstream of) the tumor necrosis factor receptor-associated factor 6 complex. Multiple proteins of the distal IL-1β-signaling pathway are subject to hydroxylation and form complexes with either prolyl hydroxylase 1 or factor inhibiting HIF. Thus, we hypothesize that hydroxylases regulate IL-1β signaling and subsequent inflammatory gene expression. Furthermore, hydroxylase inhibition represents a unique approach to the inhibition of IL-1β-dependent inflammatory signaling.
      277Scopus© Citations 145
  • Publication
    NF-B Links CO2 Sensing to Innate Immunity and Inflammation in Mammalian Cells
    (The American Association of Immunologists, 2010-09-03) ; ; ;
    Molecular O2 and CO2 are the primary substrate and product of aerobic metabolism, respectively. Levels of these physiologic gases in the cell microenvironment vary dramatically both in health and in diseases, such as chronic inflammation, ischemia, and cancer, in which metabolism is significantly altered. The identification of the hypoxia-inducible factor led to the discovery of an ancient and direct link between tissue O2 and gene transcription. In this study, we demonstrate that mammalian cells (mouse embryonic fibroblasts and others) also sense changes in local CO2 levels, leading to altered gene expression via the NF-κB pathway. IKKα, a central regulatory component of NF-κB, rapidly and reversibly translocates to the nucleus in response to elevated CO2. This response is independent of hypoxia-inducible factor hydroxylases, extracellular and intracellular pH, and pathways that mediate acute CO2-sensing in nematodes and flies and leads to attenuation of bacterial LPS-induced gene expression. These results suggest the existence of a molecular CO2 sensor in mammalian cells that is linked to the regulation of genes involved in innate immunity and inflammation.
      466Scopus© Citations 89