Imperial College London

DrAndrewCowburn

Faculty of MedicineNational Heart & Lung Institute

Senior Lecturer (Non-Clinical)
 
 
 
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a.cowburn

 
 
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535ICTEM buildingHammersmith Campus

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Summary

 

Publications

Publication Type
Year
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50 results found

Macias D, Moore S, Crosby A, Southwood M, Du X, Tan H, Xie S, Vassallo A, Wood AJ, Wallace EM, Cowburn ASet al., 2021, Targeting HIF2α-ARNT hetero-dimerisation as a novel therapeutic strategy for pulmonary arterial hypertension, European Respiratory Journal, Vol: 57, ISSN: 0903-1936

Pulmonary Arterial Hypertension (PAH) is a destructive disease of the pulmonary vasculature often leading to right heart failure and death. Current therapeutic intervention strategies only slow disease progression. The role of aberrant HIF2α stability and function in the initiation and development of pulmonary hypertension (PH) has been an area of intense interest for nearly two decades.Here we determine the effect of a novel HIF2α inhibitor (PT2567) on PH disease initiation and progression, using two pre-clinical models of PH. Haemodynamic measurements were performed followed by collection of heart, lung and blood for pathological, gene expression and biochemical analysis. Blood outgrowth endothelial cells from IPAH patients were used to determine the impact of HIF2α-inhibition on endothelial function.Global inhibition of HIF2a reduced pulmonary vascular haemodynamics and pulmonary vascular remodelling in both su5416/hypoxia prevention and intervention models. PT2567 intervention reduced the expression of PH associated target genes in both lung and cardiac tissues and restored plasma nitrite concentration. Treatment of monocrotaline exposed rodents with PT2567 reduced the impact on cardiovascular haemodynamics and promoted a survival advantage. In vitro, loss of HIF2α signalling in human pulmonary arterial endothelial cells suppresses target genes associated with inflammation, and PT2567 reduced the hyper-proliferative phenotype and over-active arginase activity in blood outgrowth endothelial cells from IPAH patients. These data suggest that targeting HIF2α hetero-dimerisation with an orally bioavailable compound could offer a new therapeutic approach for PAH. Future studies are required to determine the role of HIF in the heterogeneous PAH population.

Journal article

Gassmann M, Cowburn A, Gu H, Li J, Rodriguez M, Babicheva A, Jain PP, Xiong M, Gassmann NN, Yuan JX-J, Wilkins MR, Zhao Let al., 2021, Hypoxia-induced pulmonary hypertension - utilising experiments of nature, British Journal of Pharmacology, Vol: 178, Pages: 121-131, ISSN: 0007-1188

An increase in pulmonary artery pressure is a common observation in adult mammals exposed to global alveolar hypoxia. It is considered a maladaptive response that places an increased workload on the right ventricle. The mechanisms initiating and maintaining the elevated pressure are of considerable interest to understanding pulmonary vascular homeostasis. There is an expectation that identifying the key molecules in the integrated vascular response to hypoxia will inform potential drug targets. One strategy is to take advantage of experiments of nature; specifically, to understand the genetic basis for the inter-individual variation in the pulmonary vascular response to acute and chronic hypoxia. To date, detailed phenotyping of highlanders has focused on haematocrit and oxygen saturation rather that cardiovascular phenotypes. This review explores what we can learn from those studies with respect to the pulmonary circulation.

Journal article

Lodge KM, Cowburn AS, Li W, Condliffe AMet al., 2020, The impact of hypoxia on neutrophil degranulation and consequences for the host, International Journal of Molecular Sciences, Vol: 21, Pages: 1-21, ISSN: 1422-0067

Neutrophils are key effector cells of innate immunity, rapidly recruited to defend the host against invading pathogens. Neutrophils may kill pathogens intracellularly, following phagocytosis, or extracellularly, by degranulation and the release of neutrophil extracellular traps; all of these microbicidal strategies require the deployment of cytotoxic proteins and proteases, packaged during neutrophil development within cytoplasmic granules. Neutrophils operate in infected and inflamed tissues, which can be profoundly hypoxic. Neutrophilic infiltration of hypoxic tissues characterises a myriad of acute and chronic infectious and inflammatory diseases, and as well as potentially protecting the host from pathogens, neutrophil granule products have been implicated in causing collateral tissue damage in these scenarios. This review discusses the evidence for the enhanced secretion of destructive neutrophil granule contents observed in hypoxic environments and the potential mechanisms for this heightened granule exocytosis, highlighting implications for the host. Understanding the dichotomy of the beneficial and detrimental consequences of neutrophil degranulation in hypoxic environments is crucial to inform potential neutrophil-directed therapeutics in order to limit persistent, excessive, or inappropriate inflammation.

Journal article

De Alessandris S, Ferguson GJ, Dodd AJ, Juss JK, Devaprasad A, Piper S, Wyatt O, Killick H, Corkill DJ, Cohen ES, Pandit A, Radstake TRDJ, Simmonds R, Condliffe AM, Sleeman MA, Cowburn AS, Finch DK, Chilvers ERet al., 2019, Neutrophil GM-CSF receptor dynamics in acute lung injury, Journal of Leukocyte Biology, Vol: 105, Pages: 1183-1194, ISSN: 0741-5400

GM‐CSF is important in regulating acute, persistent neutrophilic inflammation in certain settings, including lung injury. Ligand binding induces rapid internalization of the GM‐CSF receptor (GM‐CSFRα) complex, a process essential for signaling. Whereas GM‐CSF controls many aspects of neutrophil biology, regulation of GM‐CSFRα expression is poorly understood, particularly the role of GM‐CSFRα in ligand clearance and whether signaling is sustained despite major down‐regulation of GM‐CSFRα surface expression. We established a quantitative assay of GM‐CSFRα surface expression and used this, together with selective anti‐GM‐CSFR antibodies, to define GM‐CSFRα kinetics in human neutrophils, and in murine blood and alveolar neutrophils in a lung injury model. Despite rapid sustained ligand‐induced GM‐CSFRα loss from the neutrophil surface, which persisted even following ligand removal, pro‐survival effects of GM‐CSF required ongoing ligand‐receptor interaction. Neutrophils recruited to the lungs following LPS challenge showed initially high mGM‐CSFRα expression, which along with mGM‐CSFRβ declined over 24 hr; this was associated with a transient increase in bronchoalveolar lavage fluid (BALF) mGM‐CSF concentration. Treating mice in an LPS challenge model with CAM‐3003, an anti‐mGM‐CSFRα mAb, inhibited inflammatory cell influx into the lung and maintained the level of BALF mGM‐CSF. Consistent with neutrophil consumption of GM‐CSF, human neutrophils depleted exogenous GM‐CSF, independent of protease activity. These data show that loss of membrane GM‐CSFRα following GM‐CSF exposure does not preclude sustained GM‐CSF/GM‐CSFRα signaling and that this receptor plays a key role in ligand clearance. Hence neutrophilic activation via GM‐CSFR may play an important role in neutrophilic lung inflammation even in the absence of high GM‐CSF levels or GM‐CSFRα expression.

Journal article

Macias D, Cowburn AS, Torres-Torrelo H, Ortega-Sáenz P, López-Barneo J, Johnson Ret al., 2018, Correction: HIF-2α is essential for carotid body development and function., Elife, Vol: 7

Journal article

Macias D, Cowburn AS, Torres-Torrelo H, Ortega-Sáenz P, López-Barneo J, Johnson RSet al., 2018, HIF-2α is essential for carotid body development and function, eLife, Vol: 7, ISSN: 2050-084X

Mammalian adaptation to oxygen flux occurs at many levels, from shifts in cellular metabolism to physiological adaptations facilitated by the sympathetic nervous system and carotid body (CB). Interactions between differing forms of adaptive response to hypoxia, including transcriptional responses orchestrated by the Hypoxia Inducible transcription Factors (HIFs), are complex and clearly synergistic. We show here that there is an absolute developmental requirement for HIF-2α, one of the HIF isoforms, for growth and survival of oxygen sensitive glomus cells of the carotid body. The loss of these cells renders mice incapable of ventilatory responses to hypoxia, and this has striking effects on processes as diverse as arterial pressure regulation, exercise performance, and glucose homeostasis. We show that the expansion of the glomus cells is correlated with mTORC1 activation, and is functionally inhibited by rapamycin treatment. These findings demonstrate the central role played by HIF-2α in carotid body development, growth and function.

Journal article

Sim J, Cowburn AS, Palazon A, Madhu B, Tyrakis PA, Macias D, Bargiela DM, Pietsch S, Gralla M, Evans CE, Kittipassorn T, Chey YCJ, Branco CM, Rundqvist H, Peet DJ, Johnson RSet al., 2018, The factor inhibiting HIF asparaginyl hydroxylase regulates oxidative metabolism and accelerates metabolic adaptation to hypoxia, Cell Metabolism, Vol: 27, Pages: 898-913.e7, ISSN: 1550-4131

Animals require an immediate response to oxygen availability to allow rapid shifts between oxidative and glycolytic metabolism. These metabolic shifts are highly regulated by the HIF transcription factor. The factor inhibiting HIF (FIH) is an asparaginyl hydroxylase that controls HIF transcriptional activity in an oxygen-dependent manner. We show here that FIH loss increases oxidative metabolism, while also increasing glycolytic capacity, and that this gives rise to an increase in oxygen consumption. We further show that the loss of FIH acts to accelerate the cellular metabolic response to hypoxia. Skeletal muscle expresses 50-fold higher levels of FIH than other tissues: we analyzed skeletal muscle FIH mutants and found a decreased metabolic efficiency, correlated with an increased oxidative rate and an increased rate of hypoxic response. We find that FIH, through its regulation of oxidation, acts in concert with the PHD/vHL pathway to accelerate HIF-mediated metabolic responses to hypoxia.

Journal article

Cowburn AS, Macias D, Summers C, Chilvers ER, Johnson RSet al., 2017, Cardiovascular adaptation to hypoxia and the role of peripheral resistance, eLife, Vol: 6, ISSN: 2050-084X

Systemic vascular pressure in vertebrates is regulated by a range of factors: one key element of control is peripheral resistance in tissue capillary beds. Many aspects of the relationship between central control of vascular flow and peripheral resistance are unclear. An important example of this is the relationship between hypoxic response in individual tissues, and the effect that response has on systemic cardiovascular adaptation to oxygen deprivation. We show here how hypoxic response via the HIF transcription factors in one large vascular bed, that underlying the skin, influences cardiovascular response to hypoxia in mice. We show that the response of the skin to hypoxia feeds back on a wide range of cardiovascular parameters, including heart rate, arterial pressures, and body temperature. These data represent the first demonstration of a dynamic role for oxygen sensing in a peripheral tissue directly modifying cardiovascular response to the challenge of hypoxia.

Journal article

Pocock JM, Storisteanu DML, Reeves MB, Juss JK, Wills MR, Cowburn AS, Chilvers ERet al., 2017, Human Cytomegalovirus Delays Neutrophil Apoptosis and Stimulates the Release of a Prosurvival Secretome, FRONTIERS IN IMMUNOLOGY, Vol: 8, ISSN: 1664-3224

Human cytomegalovirus (HCMV) is a major cause of viral disease in the young and the immune-suppressed. At sites of infection, HCMV recruits the neutrophil, a cell with a key role in orchestrating the initial immune response. Herein, we report a profound survival response in human neutrophils exposed to the clinical HCMV isolate Merlin, but not evident with the attenuated strain AD169, through suppression of apoptosis. The initial survival event, which is independent of viral gene expression and involves activation of the ERK/MAPK and NF-κB pathways, is augmented by HCMV-stimulated release of a secretory cytokine profile that further prolongs neutrophil lifespan. As aberrant neutrophil survival contributes to tissue damage, we predict that this may be relevant to the immune pathology of HCMV, and the presence of this effect in clinical HCMV strains and its absence in attenuated strains implies a beneficial effect to the virus in pathogenesis and/or dissemination. In addition, we show that HCMV-exposed neutrophils release factors that enhance monocyte recruitment and drive monocyte differentiation to a HCMV-permissive phenotype in an IL-6-dependent manner, thus providing an ideal vehicle for viral dissemination. This study increases understanding of HCMV–neutrophil interactions, highlighting the potential role of neutrophil recruitment as a virulence mechanism to promote HCMV pathology in the host and influence the dissemination of HCMV infection. Targeting these mechanisms may lead to new antiviral strategies aimed at limiting host damage and inhibiting viral spread.

Journal article

Siebenmann C, Keramidas ME, Rundqvist H, Mijwel S, Cowburn AS, Johnson RS, Eiken Oet al., 2017, Cutaneous exposure to hypoxia does not affect skin perfusion in humans, ACTA PHYSIOLOGICA, Vol: 220, Pages: 361-369, ISSN: 1748-1708

Journal article

Porter LM, Cowburn AS, Farahi N, Deighton J, Farrow SN, Fiddler CA, Juss JK, Condliffe AM, Chilvers ERet al., 2017, Hypoxia causes IL-8 secretion, Charcot Leyden crystal formation, and suppression of corticosteroid-induced apoptosis in human eosinophils, Clinical and Experimental Allergy, Vol: 47, Pages: 770-784, ISSN: 0954-7894

BackgroundInflamed environments are typically hypercellular, rich in pro‐inflammatory cytokines, and profoundly hypoxic. While the effects of hypoxia on neutrophil longevity and function have been widely studied, little is known about the consequences of this stimulus on eosinophils.ObjectiveWe sought to investigate the effects of hypoxia on several key aspects of eosinophil biology, namely secretion, survival, and their sensitivity to glucocorticosteroids (GCS), agents that normally induce eosinophil apoptosis.MethodsEosinophils derived from patients with asthma/atopy or healthy controls were incubated under normoxia and hypoxia, with or without glucocorticoids. Activation was measured by flow cytometry, ELISA of cultured supernatants, and F‐actin staining; apoptosis and efferocytosis by morphology and flow cytometry; and GCS efficacy by apoptosis assays and qPCR.ResultsHypoxic incubation (3 kPa) caused (i) stabilization of HIF‐2α and up‐regulation of hypoxia‐regulated genes including BNIP3 (BCL2/adenovirus E1B 19‐kDa protein‐interacting protein 3) and GLUT1 (glucose transporter 1); (ii) secretion of pre‐formed IL‐8, and Charcot Leyden crystal (CLC) formation, which was most evident in eosinophils derived from atopic and asthmatic donors; (iii) enhanced F‐actin formation; (iv) marked prolongation of eosinophil lifespan (via a NF‐κB and Class I PI3‐kinase‐dependent mechanism); and (v) complete abrogation of the normal pro‐apoptotic effect of dexamethasone and fluticasone furoate. This latter effect was evident despite preservation of GCS‐mediated gene transactivation under hypoxia.Conclusion and Clinical RelevanceThese data indicate that hypoxia promotes an eosinophil pro‐inflammatory phenotype by enhancing eosinophil secretory function, delaying constitutive apoptosis, and importantly, antagonizing the normal pro‐apoptotic effect of GCS. As eosinophils typically accumulate at sites that are relatively hypoxic, particularly during periods of inflammation

Journal article

Storisteanu DML, Pocock JM, Cowburn AS, Juss JK, Nadesalingam A, Nizet V, Chilvers ERet al., 2017, Evasion of neutrophil extracellular traps by respiratory pathogens, American Journal of Respiratory Cell and Molecular Biology, Vol: 56, Pages: 423-431, ISSN: 1044-1549

The release of neutrophil extracellular traps (NETs) is a major immune mechanism intended to capture pathogens. These histone- and protease-coated DNA structures are released by neutrophils in response to a variety of stimuli, including respiratory pathogens, and have been identified in the airways of patients with respiratory infection, cystic fibrosis, acute lung injury, primary graft dysfunction, and chronic obstructive pulmonary disease. NET production has been demonstrated in the lungs of mice infected with Staphylococcus aureus, Klebsiella pneumoniae, and Aspergillus fumigatus. Since the discovery of NETs over a decade ago, evidence that “NET evasion” might act as an immune protection strategy among respiratory pathogens, including group A Streptococcus, Bordetella pertussis, and Haemophilus influenzae, has been growing, with the majority of these studies being published in the past 2 years. Evasion strategies fall into three main categories: inhibition of NET release by down-regulating host inflammatory responses; degradation of NETs using pathogen-derived DNases; and resistance to the microbicidal components of NETs, which involves a variety of mechanisms, including encapsulation. Hence, the evasion of NETs appears to be a widespread strategy to allow pathogen proliferation and dissemination, and is currently a topic of intense research interest. This article outlines the evidence supporting the three main strategies of NET evasion—inhibition, degradation, and resistance—with particular reference to common respiratory pathogens.

Journal article

Thompson AAR, Dickinson RS, Murphy F, Thomson JP, Marriott HM, Tavares A, Willson J, Williams L, Lewis A, Mirchandani A, Coelho PDS, Doherty C, Ryan E, Watts E, Morton NM, Forbes S, Stimson RH, Hameed AG, Arnold N, Preston JA, Lawrie A, Finisguerra V, Mazzone M, Sadiku P, Goveia J, Taverna F, Carmeliet P, Foster SJ, Chilvers ER, Cowburn AS, Dockrell DH, Johnson RS, Meehan RR, Whyte MKB, Walmsley SRet al., 2017, Hypoxia determines survival outcomes of bacterial infection through HIF-1 alpha-dependent reprogramming of leukocyte metabolism, Science Immunology, Vol: 2, Pages: 1-12, ISSN: 2470-9468

Hypoxia and bacterial infection frequently coexist, in both acute and chronic clinical settings, and typically result in adverse clinical outcomes. To ameliorate this morbidity, we investigated the interaction between hypoxia and the host response. In the context of acute hypoxia, both Staphylococcus aureus and Streptococcus pneumoniae infections rapidly induced progressive neutrophil-mediated morbidity and mortality, with associated hypothermia and cardiovascular compromise. Preconditioning animals through longer exposures to hypoxia, before infection, prevented these pathophysiological responses and profoundly dampened the transcriptome of circulating leukocytes. Specifically, perturbation of hypoxia-inducible factor (HIF) pathway and glycolysis genes by hypoxic preconditioning was associated with reduced leukocyte glucose utilization, resulting in systemic rescue from a global negative energy state and myocardial protection. Thus, we demonstrate that hypoxia preconditions the innate immune response and determines survival outcomes after bacterial infection through suppression of HIF-1α and neutrophil metabolism. In the context of systemic or tissue hypoxia, therapies that target the host response could improve infection-associated morbidity and mortality.

Journal article

Cowburn AS, Crosby A, Macias D, Branco C, Colaco RDDR, Southwood M, Toshner M, Alexander LEC, Morrell NW, Chilvers ER, Johnson RSet al., 2016, HIF2 alpha-arginase axis is essential for the development of pulmonary hypertension, Proceedings of the National Academy of Sciences of the United States of America, Vol: 113, Pages: 8801-8806, ISSN: 0027-8424

Hypoxic pulmonary vasoconstriction is correlated with pulmonary vascular remodeling. The hypoxia-inducible transcription factors (HIFs) HIF-1α and HIF-2α are known to contribute to the process of hypoxic pulmonary vascular remodeling; however, the specific role of pulmonary endothelial HIF expression in this process, and in the physiological process of vasoconstriction in response to hypoxia, remains unclear. Here we show that pulmonary endothelial HIF-2α is a critical regulator of hypoxia-induced pulmonary arterial hypertension. The rise in right ventricular systolic pressure (RVSP) normally observed following chronic hypoxic exposure was absent in mice with pulmonary endothelial HIF-2α deletion. The RVSP of mice lacking HIF-2α in pulmonary endothelium after exposure to hypoxia was not significantly different from normoxic WT mice and much lower than the RVSP values seen in WT littermate controls and mice with pulmonary endothelial deletion of HIF-1α exposed to hypoxia. Endothelial HIF-2α deletion also protected mice from hypoxia remodeling. Pulmonary endothelial deletion of arginase-1, a downstream target of HIF-2α, likewise attenuated many of the pathophysiological symptoms associated with hypoxic pulmonary hypertension. We propose a mechanism whereby chronic hypoxia enhances HIF-2α stability, which causes increased arginase expression and dysregulates normal vascular NO homeostasis. These data offer new insight into the role of pulmonary endothelial HIF-2α in regulating the pulmonary vascular response to hypoxia.

Journal article

Fiddler CA, Parfrey H, Cowburn AS, Luo D, Nash GB, Murphy G, Chilvers ERet al., 2016, The Aminopeptidase CD13 Induces Homotypic Aggregation in Neutrophils and Impairs Collagen Invasion, PLOS ONE, Vol: 11, ISSN: 1932-6203

Aminopeptidase N (CD13) is a widely expressed cell surface metallopeptidase involved in the migration of cancer and endothelial cells. Apart from our demonstration that CD13 modulates the efficacy of tumor necrosis factor-α-induced apoptosis in neutrophils, no other function for CD13 has been ascribed in this cell. We hypothesized that CD13 may be involved in neutrophil migration and/or homotypic aggregation. Using purified human blood neutrophils we confirmed the expression of CD13 on neutrophils and its up-regulation by pro-inflammatory agonists. However, using the anti-CD13 monoclonal antibody WM-15 and the aminopeptidase enzymatic inhibitor bestatin we were unable to demonstrate any direct involvement of CD13 in neutrophil polarisation or chemotaxis. In contrast, IL-8-mediated neutrophil migration in type I collagen gels was significantly impaired by the anti-CD13 monoclonal antibodies WM-15 and MY7. Notably, these antibodies also induced significant homotypic aggregation of neutrophils, which was dependent on CD13 cross-linking and was attenuated by phosphoinositide 3-kinase and extracellular signal-related kinase 1/2 inhibition. Live imaging demonstrated that in WM-15-treated neutrophils, where homotypic aggregation was evident, the number of cells entering IL-8 impregnated collagen I gels was significantly reduced. These data reveal a novel role for CD13 in inducing homotypic aggregation in neutrophils, which results in a transmigration deficiency; this mechanism may be relevant to neutrophil micro-aggregation in vivo.

Journal article

Semba H, Takeda N, Isagawa T, Sugiura Y, Honda K, Wake M, Miyazawa H, Yamaguchi Y, Miura M, Jenkins DMR, Choi H, Kim J-W, Asagiri M, Cowburn AS, Abe H, Soma K, Koyama K, Katoh M, Sayama K, Goda N, Johnson RS, Manabe I, Nagai R, Komuro Iet al., 2016, HIF-1 alpha-PDK1 axis-induced active glycolysis plays an essential role in macrophage migratory capacity, Nature Communications, Vol: 7, Pages: 1-10, ISSN: 2041-1723

In severely hypoxic condition, HIF-1α-mediated induction of Pdk1 was found to regulate glucose oxidation by preventing the entry of pyruvate into the tricarboxylic cycle. Monocyte-derived macrophages, however, encounter a gradual decrease in oxygen availability during its migration process in inflammatory areas. Here we show that HIF-1α-PDK1-mediated metabolic changes occur in mild hypoxia, where mitochondrial cytochrome c oxidase activity is unimpaired, suggesting a mode of glycolytic reprogramming. In primary macrophages, PKM2, a glycolytic enzyme responsible for glycolytic ATP synthesis localizes in filopodia and lammelipodia, where ATP is rapidly consumed during actin remodelling processes. Remarkably, inhibition of glycolytic reprogramming with dichloroacetate significantly impairs macrophage migration in vitro and in vivo. Furthermore, inhibition of the macrophage HIF-1α-PDK1 axis suppresses systemic inflammation, suggesting a potential therapeutic approach for regulating inflammatory processes. Our findings thus demonstrate that adaptive responses in glucose metabolism contribute to macrophage migratory activity.

Journal article

Ashmore T, Roberts LD, Morash AJ, Kotwica AO, Finnerty J, West JA, Murfitt SA, Fernandez BO, Branco C, Cowburn AS, Clarke K, Johnson RS, Feelisch M, Griffin JL, Murray AJet al., 2015, Nitrate enhances skeletal muscle fatty acid oxidation via a nitric oxide-cGMP-PPAR-mediated mechanism, BMC Biology, Vol: 13, Pages: 1-17, ISSN: 1741-7007

BackgroundInsulin sensitivity in skeletal muscle is associated with metabolic flexibility, including a high capacity to increase fatty acid (FA) oxidation in response to increased lipid supply. Lipid overload, however, can result in incomplete FA oxidation and accumulation of potentially harmful intermediates where mitochondrial tricarboxylic acid cycle capacity cannot keep pace with rates of β-oxidation. Enhancement of muscle FA oxidation in combination with mitochondrial biogenesis is therefore emerging as a strategy to treat metabolic disease. Dietary inorganic nitrate was recently shown to reverse aspects of the metabolic syndrome in rodents by as yet incompletely defined mechanisms.ResultsHerein, we report that nitrate enhances skeletal muscle FA oxidation in rodents in a dose-dependent manner. We show that nitrate induces FA oxidation through a soluble guanylate cyclase (sGC)/cGMP-mediated PPARβ/δ- and PPARα-dependent mechanism. Enhanced PPARβ/δ and PPARα expression and DNA binding induces expression of FA oxidation enzymes, increasing muscle carnitine and lowering tissue malonyl-CoA concentrations, thereby supporting intra-mitochondrial pathways of FA oxidation and enhancing mitochondrial respiration. At higher doses, nitrate induces mitochondrial biogenesis, further increasing FA oxidation and lowering long-chain FA concentrations. Meanwhile, nitrate did not affect mitochondrial FA oxidation in PPARα−/− mice. In C2C12 myotubes, nitrate increased expression of the PPARα targets Cpt1b, Acadl, Hadh and Ucp3, and enhanced oxidative phosphorylation rates with palmitoyl-carnitine; however, these changes in gene expression and respiration were prevented by inhibition of either sGC or protein kinase G. Elevation of cGMP, via the inhibition of phosphodiesterase 5 by sildenafil, also increased expression of Cpt1b, Acadl and Ucp3, as well as CPT1B protein levels, and further enhanced the effect of nitrate s

Journal article

Cheng JPX, Mendoza-Topaz C, Howard G, Chadwick J, Shvets E, Cowburn AS, Dunmore BJ, Crosby A, Morrell NW, Nichols BJet al., 2015, Caveolae protect endothelial cells from membrane rupture during increased cardiac output, JOURNAL OF CELL BIOLOGY, Vol: 211, Pages: 53-61, ISSN: 0021-9525

Journal article

Ashmore T, Fernandez BO, Branco-Price C, West JA, Cowburn AS, Heather LC, Griffin JL, Johnson RS, Feelisch M, Murray AJet al., 2014, Dietary nitrate increases arginine availability and protects mitochondrial complex I and energetics in the hypoxic rat heart, JOURNAL OF PHYSIOLOGY-LONDON, Vol: 592, Pages: 4715-4731, ISSN: 0022-3751

Hypoxic exposure is associated with impaired cardiac energetics in humans and altered mitochondrial function, with suppressed complex I‐supported respiration, in rat heart. This response might limit reactive oxygen species generation, but at the cost of impaired electron transport chain (ETC) activity. Dietary nitrate supplementation improves mitochondrial efficiency and can promote tissue oxygenation by enhancing blood flow. We therefore hypothesised that ETC dysfunction, impaired energetics and oxidative damage in the hearts of rats exposed to chronic hypoxia could be alleviated by sustained administration of a moderate dose of dietary nitrate. Male Wistar rats (n = 40) were given water supplemented with 0.7 mmol l−1 NaCl (as control) or 0.7 mmol l−1 NaNO3, elevating plasma nitrate levels by 80%, and were exposed to 13% O2 (hypoxia) or normoxia (n = 10 per group) for 14 days. Respiration rates, ETC protein levels, mitochondrial density, ATP content and protein carbonylation were measured in cardiac muscle. Complex I respiration rates and protein levels were 33% lower in hypoxic/NaCl rats compared with normoxic/NaCl controls. Protein carbonylation was 65% higher in hearts of hypoxic rats compared with controls, indicating increased oxidative stress, whilst ATP levels were 62% lower. Respiration rates, complex I protein and activity, protein carbonylation and ATP levels were all fully protected in the hearts of nitrate‐supplemented hypoxic rats. Both in normoxia and hypoxia, dietary nitrate suppressed cardiac arginase expression and activity and markedly elevated cardiac l‐arginine concentrations, unmasking a novel mechanism of action by which nitrate enhances tissue NO bioavailability. Dietary nitrate therefore alleviates metabolic abnormalities in the hypoxic heart, improving myocardial energetics.

Journal article

Cowburn AS, Alexander LEC, Southwood M, Nizet V, Chilvers ER, Johnson RSet al., 2014, Epidermal deletion of HIF-2 alpha stimulates wound closure, Journal of Investigative Dermatology, Vol: 134, Pages: 801-808, ISSN: 0022-202X

Wound closure requires a complex series of micro-environmentally influenced events. A key aspect of wound closure is the migration of keratinocytes across the open wound. It has been found previously that the response to hypoxia via the HIF-1α transcription factor is a key feature of wound closure. The need for hypoxic response is likely due to interrupted wound vasculature, as well as infection, and in this work we investigated the need for a highly related hypoxic response transcription factor, HIF-2α. This factor was deleted tissue specifically in mice, and the resulting mice were found to have an accelerated rate of wound closure. This is correlated with a reduced bacterial load and inflammatory response in these mice. This indicates that manipulating or reducing the HIF-2α response in keratinocytes could be a useful means to accelerate wound healing and tissue repair.

Journal article

Cowburn AS, Takeda N, Boutin AT, Kim J-W, Sterling JC, Nakasaki M, Southwood M, Goldrath AW, Jamora C, Nizet V, Chilvers ER, Johnson RSet al., 2013, HIF isoforms in the skin differentially regulate systemic arterial pressure, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol: 110, Pages: 17570-17575, ISSN: 0027-8424

Journal article

Alexander LEC, Akong-Moore K, Feldstein S, Johansson P, Anh N, McEachern EK, Nicatia S, Cowburn AS, Olson J, Cho JY, Isaacs H, Johnson RS, Broide DH, Nizet Vet al., 2013, Myeloid cell HIF-1 alpha regulates asthma airway resistance and eosinophil function, JOURNAL OF MOLECULAR MEDICINE-JMM, Vol: 91, Pages: 637-644, ISSN: 0946-2716

Journal article

Juss JK, Hayhoe RP, Owen CE, Bruce I, Walmsley SR, Cowburn AS, Kulkarni S, Boyle KB, Stephens L, Hawkins PT, Chilvers ER, Condliffe AMet al., 2012, Functional redundancy of class I phosphoinositide 3-kinase (PI3K) isoforms in signaling growth factor-mediated human neutrophil survival, PLoS One, Vol: 7, Pages: 1-15, ISSN: 1932-6203

We have investigated the contribution of individual phosphoinositide 3-kinase (PI3K) Class I isoforms to the regulation of neutrophil survival using (i) a panel of commercially available small molecule isoform-selective PI3K Class I inhibitors, (ii) novel inhibitors, which target single or multiple Class I isoforms (PI3Kα, PI3Kβ, PI3Kδ, and PI3Kγ), and (iii) transgenic mice lacking functional PI3K isoforms (p110δKOγKO or p110γKO). Our data suggest that there is considerable functional redundancy amongst Class I PI3Ks (both Class IA and Class IB) with regard to GM-CSF-mediated suppression of neutrophil apoptosis. Hence pharmacological inhibition of any 3 or more PI3K isoforms was required to block the GM-CSF survival response in human neutrophils, with inhibition of individual or any two isoforms having little or no effect. Likewise, isolated blood neutrophils derived from double knockout PI3K p110δKOγKO mice underwent normal time-dependent constitutive apoptosis and displayed identical GM-CSF mediated survival to wild type cells, but were sensitized to pharmacological inhibition of the remaining PI3K isoforms. Surprisingly, the pro-survival neutrophil phenotype observed in patients with an acute exacerbation of chronic obstructive pulmonary disease (COPD) was resilient to inactivation of the PI3K pathway.

Journal article

White JF, Cowburn AS, Summers C, Cadwallader KA, Mackenzie I, Praseedom RK, Chilvers ER, Peters AMet al., 2011, The influence of the spleen on neutrophil apoptosis in vivo, Journal of Cell Death, Vol: 2011, Pages: 1-5

In contrast to radiolabelled erythrocytes and platelets, radiolabelled neutrophils leave the circulating blood in an exponential manner, indicating random rather than age-dependent removal. Neutrophils transit the spleen with a range of residence times that are log normally distributed. We hypothesized that neutrophils are conditioned to undergo apoptosis to an extent that depends on their intrasplenic residence time and that this provides an explanation for the random removal of these cells from blood. Splenic venous and peripheral arterial blood was sampled simultaneously during abdominal surgery in four patients and age-dependent apoptosis assessed in whole blood using annexin V/PI staining. Apoptosis increased after 4 and 20h ex-vivo incubation and was invariably higher in splenic venous vs arterial neutrophils. Transit through the spleen appears to promote neutrophil apoptosis, with subsequent high efficiency clearance by the liver. This may explain the mechanism underlying the random removal of neutrophils from the blood. © the author(s).

Journal article

Cowburn AS, Summers C, Dunmore BJ, Farahi N, Hayhoe RP, Print CG, Cook SJ, Chilvers ERet al., 2011, Granulocyte/Macrophage Colony-Stimulating Factor Causes a Paradoxical Increase in the BH3-Only Pro-Apoptotic Protein Bim in Human Neutrophils, AMERICAN JOURNAL OF RESPIRATORY CELL AND MOLECULAR BIOLOGY, Vol: 44, Pages: 879-887, ISSN: 1044-1549

Journal article

Farahi N, Uller L, Juss JK, Langton AJ, Cowburn AS, Gibson A, Foster MR, Farrow SN, Marco-Casanova P, Sobolewski A, Condliffe AM, Chilvers ERet al., 2011, Effects of the cyclin-dependent kinase inhibitor R-roscovitine on eosinophil survival and clearance, CLINICAL AND EXPERIMENTAL ALLERGY, Vol: 41, Pages: 673-687, ISSN: 0954-7894

Journal article

Roe MFE, Bloxham DM, Cowburn AS, O'Donnell DRet al., 2011, Changes in helper lymphocyte chemokine receptor expression and elevation of IP-10 during acute respiratory syncytial virus infection in infants, PEDIATRIC ALLERGY AND IMMUNOLOGY, Vol: 22, Pages: 229-234, ISSN: 0905-6157

Journal article

McGovern NN, Cowburn AS, Porter L, Walmsley SR, Summers C, Thompson AAR, Anwar S, Willcocks LC, Whyte MKB, Condliffe AM, Chilvers ERet al., 2011, Hypoxia Selectively Inhibits Respiratory Burst Activity and Killing of Staphylococcus aureus in Human Neutrophils, JOURNAL OF IMMUNOLOGY, Vol: 186, Pages: 453-463, ISSN: 0022-1767

Journal article

Brode S, Farahi N, Cowburn AS, Juss JK, Condliffe AM, Chilvers ERet al., 2010, Interleukin-5 inhibits glucocorticoid-mediated apoptosis in human eosinophils, THORAX, Vol: 65, Pages: 1116-1117, ISSN: 0040-6376

Journal article

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