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Carbon dioxide detection in biological systems

Scientific meeting

Location

Kavli Royal Society Centre, Chicheley Hall, Newport Pagnell, Buckinghamshire, MK16 9JJ

Overview

Theo Murphy international scientific meeting organised by Professor Martin Cann, Dr Vicki Linthwaite and Dr Eoin Cummins.

Immunocytochemistry image of soluble adenylyl cyclase in trout fibroblasts. Provided by Drs Cristina Salmeron and Martin Tresguerres.

This meeting will unite researchers from the plant and animal kingdoms to discuss the common goal of understanding the molecular basis of carbon dioxide detection.

Carbon dioxide is essential for life on earth. It is central to physiological processes including photosynthesis, metabolism, homeostasis, chemosensing and pathogenesis. Given recent and rapid developments in our understanding of mechanisms that underpin carbon dioxide detection in both the plant and animal kingdoms, a new forum must be developed to bring together researchers in these fields.

This forum will identify common themes in carbon dioxide detection across different biological systems and exchange methodologies that can be bought to bear on different biological systems. Furthermore, its members will identify new approaches that can benefit our identification of carbon dioxide detection mechanisms across diverse species. The forum will foster the creation of new scientific community/network that will enhance the pursuit of knowledge in this area and form the foundations for future collaborative publications and funding proposals.

Speaker abstracts will be available closer to the meeting. Recorded audio of the presentations will be available on this page after the meeting has taken place.

Meeting papers will be published in a future issue of Interface Focus.

Poster session

There will be a poster session at 17:00 on Monday 2 December 2019. If you would like to apply to present a poster please submit your proposed title, abstract (not more than 200 words and must be in third person), author list, name of the proposed presenter and institution to the Scientific Programmes team with the subject heading "Carbon Dioxide: poster abstract" no later than Friday 18 October 2019.

Please note that places are limited and posters are selected at the scientific organisers' discretion. Poster abstracts will only be considered if the presenter is registered to attend the meeting.

Attending this event

This is a residential conference, which allows for increased discussion and networking.

  • Free to attend
  • Limited places
  • Please request a registration invitation above
  • Catering and accommodation available to purchase during registration

Enquiries: contact the Scientific Programmes team

Event organisers

Select an organiser for more information

Schedule of talks

02 December

09:00-12:15

Session 1

10 talks Show detail Hide detail

Chairs

Professor Martin Cann, Durham University, UK

09:00-09:05 Welcome by the Royal Society and organisers

09:05-09:35 Protein carbamylation: the discovery of a carbon dioxide control system

Dr Vicki Linthwaite, Durham University, UK

Abstract

Carbon dioxide (CO2) is fundamental to life with critical roles in respiration, photosynthesis and acid-base homeostasis. Carbamates are formed rapidly but reversibly by the nucleophilic attack of an uncharged amine on CO2 at physiological temperatures and pressures. The  presence  of  this  post-translational  modification  has  been  demonstrated  in  a  small  number  of key  proteins,  such  as  RuBisCO  and  haemoglobin. 

The systematic identification of carbamates has been hindered due to their labile nature, therefore previous work has involved their study under non-physiological conditions. We have developed a novel technology using a chemical trapping technique to covalently modify carbamates and remove their labile nature1. This has been combined with downstream proteomic analysis via tryptic digest and ESI-MS to validate the carbamate modifications identified.

Our method successfully identified the haemoglobin carbamate binding site under physiologically relevant conditions. These results were confirmed using ESI-MS combined with 12C and 13C isotope incorporation. This research has produced a method that utilises a pre-existing chemical reagent to remove the labile nature of carbamates and thereby provides the first description of systematic carbamate identification in a physiologically relevant environment. 

Screening of mammalian protein lysate identified two sites on the ubiquitin protein which were able to bind CO2. Carbamylation of ubiquitin has been demonstrated directly to influence the protein ubiquitin cross linking at this site in vitro and in cellulo. We propose ubiquitin as a universal target able to mediate the diverse cellular affects of CO2.

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09:35-09:45 Discussion

09:45-10:15 Stomatal responses to carbon dioxide

Professor Alistair Hetherington, Bristol University, UK

Abstract

In response to elevated concentrations of carbon dioxide the pores on the surfaces of leaves known as stomata close. Closure restricts the loss of water vapour from the plant and the uptake of CO2 from the atmosphere.The stomatal pore is surrounded by two specialised cells known as guard cells. When guard cells lose turgor the stomatal pore closes.Research over the past 20 years has begun to identify the elements of the intracellular signal transduction pathway responsible for coupling CO2 perception with reductions in guard cell turgor. The picture emerging is that some signalling components are shared with the signalling pathways used by other closure-inducing signals while others are restricted to the CO2 response. This lecture will focus on recently identified components and on the role of the closure-inducing plant hormone abscisic acid in the guard cell CO2 response.

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10:15-10:25 Discussion

10:25-10:55 Coffee

10:55-11:25 Therapeutically targeting CO2/HCO3/pH sensing soluble adenylyl cyclase

Professor Lonny Levin, Weill Medical College of Cornell University, USA

Abstract

Signaling via the prototypical second messenger cyclic AMP (cAMP) is compartmentalized; it mediates its various responses via multiple, independently regulated cAMP signaling microdomains. Cyclic AMP is produced by adenylyl cyclases (ACs), and in mammalian cells, there are two distinct families of ACs; G protein regulated transmembrane adenylyl cyclases (tmAC) and soluble adenylyl cyclase (sAC). TmACs anchor cAMP signaling microdomains at the plasma membrane, where they respond to hormonal signals operating via G protein coupled receptors. In contrast, sAC can be found distributed throughout the cytoplasm and inside cellular organelles where it defines multiple, independently regulated intracellular cAMP signaling microdomains. sAC is also biochemically distinct from tmACs; sAC activity is uniquely and directly regulated by bicarbonate (HCO3-) ions. Due to the ubiquitous presence of carbonic anhydrases (CA), which catalyze the instantaneous equilibration of carbon dioxide (CO2), HCO3-, and protons, mammalian sAC, and its HCO3--regulated orthologs throughout the kingdoms of life, serve as Nature’s physiological CO2/HCO3-/pHi sensors. The mechanism of bicarbonate regulation of sAC, along with recent advances in pharmacological modulators, including potential novel therapeutic uses, will be discussed.

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11:25-11:35 Discussion

11:35-12:05 CO2 sensing and behaviour in insects

Professor Anandasankar Ray, University of California, Riverside, USA

Abstract

Many insects can smell CO2 using specialised seven transmembrane receptors present in olfactory neurons. In the case of blood-feeding insects like mosquitoes, the sensing of a turbulent plume of CO2 indicates a living vertebrate upwind and leads to a series of important behaviours that are critical for host-seeking. First, even a brief turbulent plume of CO2 causes the insect to activate and initiate upwind flight. Second, the flying insect utilizes the plumes of CO2 to navigate upwind towards the source. And third, the exposure to CO2 increases the behavioural attraction to odorants from human skin and to heat and visual stimuli by several fold. Results will be presented on how the conserved transmembrane heteromeric receptor proteins detect CO2, and how it can be modulated by the presence or absence of certain protein subunits. Several other classes of volatile chemicals have been identified that can act as agonists, inverse-agonists or antagonists of the CO2-receptor and showed how they can predictably alter insect behaviour. Machine learning based algorithms have been applied to screen millions of molecules for such activities on the receptor and their utility validated with electrophysiology recordings and behaviour assays. Several lines of evidence have also been uncovered which point to additional roles of the CO2-receptor in detecting other behaviourally relevant odorants and act as one of the central detectors of volatiles for olfactory behaviour in a number of flying insects. 

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12:05-12:15 Discussion

12:15-13:15

Lunch

13:15-17:00

Session 2

10 talks Show detail Hide detail

Chairs

Dr Eoin Cummins, University College Dublin, Ireland

13:15-13:45 CO2 transport

Professor Walter Boron, Case Western Reserve University, USA

Abstract

The dogma had been that all gases cross all membranes by dissolving in and diffusing through the lipid phase. Work over the past two decades shows that some membranes have negligible CO2 permeability, and that some membrane proteins—a subset of aquaporins (AQPs) and rhesus (Rh) proteins—can conduct CO2 or other gases. Preliminary data on Xenopus oocytes expressing AQP5 show that CO2 transport through AQP5 increases markedly with injection into the cytosol of small amounts of carbonic anhydrase II (CAII). The approach is to measure alkaline surface pH (pHS) transients during introduction of extracellular CO2/HCO3−. The alkaline pHS spike is greatest early, when the inward CO2 gradient—and thus the extracellular reaction HCO3− + H+  H2O + CO2—is greatest, and wanes as CO2 equilibrates across the cell membrane. Cytosolic CAII promotes the consumption of incoming CO2, thereby maintaining low cytosolic [CO2], maximizing the gradient for CO2 influx, and increasing pHS—far more so in AQP5-expressing than in control oocytes. In additional pHS experiments, the electrogenic Na/HCO3 cotransporter NBCe1 (or electroneutral NBCn1) replaced the AQP5. Earlier preliminary work based on intracellular-pH measurements had suggested that NBCe1 conducts CO2. Now, exposing oocytes expressing NBCe1 (or NBCn1)—without injected CAII—to CO2/HCO3− produces a small transient pHS increase (due to CO2 influx) followed by a large pHS decrease (CO3= uptake). In oocytes expressing NBCe1 or NBCn1, CAII injection markedly accentuates the early transient pHS increase (as for AQP5-expressing oocytes), supporting the hypothesis that NBCe1 and NBCn1 both conduct CO2.

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13:45-13:55 Discussion

13:55-14:25 The Calvin Benson cycle – atmospheric CO2 assimilation and prospects for improvement

Professor Christine Raines, Essex University, UK

Abstract

The photosynthetic carbon reduction (Calvin-Benson) cycle is the primary pathway of atmospheric CO2 assimilation in all photosynthetic organisms. It is the single largest flux of organic carbon in the biosphere, and assimilates about 100 bn tons of carbon a year (15% of the carbon in the atmosphere). Evidence has now accumulated showing that by increasing flow of CO2 through this cycle we can also increase plant yield which has the potential to contribute the future demands of an increasing world population. Analyses of transgenic with altered level of enzymes in the Calvin-Benson cycle has demonstrated the potential for increasing crop productivity through increased rates of photosynthesis and the manipulation of the allocation of photosynthate. This lecture will discuss these approaches and the future potential.

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14:25-14:35 Discussion

14:35-15:00 Tea

15:00-15:30 CO2 and lung airway function

Dr Masahiko Shigemura, Northwestern University, USA

Abstract

Carbon dioxide (CO2), a primary product of oxidative metabolism, can be sensed by eukaryotic cells eliciting specific responses via specific signaling pathways. The physiological and pathophysiological effects of high CO2 conditions (hypercapnia) on the lungs and specific lung cells, which are the primary site of CO2 elimination, are incompletely understood. Dr Shigemura’s group has recently reported using combined unbiased molecular approaches with studies in mice and cell culture systems on the mechanisms by which hypercapnia increased airway smooth muscle contractility. The group described that high CO2 levels cause non-apoptotic caspase-7 activation via the calcium-calpain signal, which cleaves the transcription factor myocyte-specific enhancer factor 2D and in turn downregulates miR-133a that increases RhoA protein abundance and myosin light chain phosphorylation, and thus leads to airway smooth muscle contraction. In demonstration of the clinical relevance of this signaling, the group determined that patients with severe chronic obstructive pulmonary disease (COPD) and hypercapnia had elevated airway resistance, which improved after correction of hypercapnia. These data suggest that hypercapnia is not only a manifestation of severe COPD, but it can also worsen the airflow obstruction.  Dr Shigemura will provide a pathophysiological and mechanistic perspective on the effects of hypercapnia on the lung airways and discuss the recent understanding of high CO2 modulation of the airway function.

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15:30-15:40 Discussion

15:40-16:10 CO2 sensing and signal transduction in stomatal guard cells

Professor Julian Schroeder, University of Calfornia, San Diego, USA

Abstract

Plants control CO2 exchange and water loss via stomatal pores. Previous research has suggested that bicarbonate (HCO3-) may directly up-regulate reconstituted SLAC1 channel activity in vitro. However, whether this HCO3- regulation is relevant in planta remains unknown. We have computationally predicted candidate bicarbonate-binding sites within SLAC1 through long-timescale Gaussian-accelerated molecular dynamics (GaMD) simulations. Gas exchange and patch clamp experiments with complemented slac1 mutant plants expressing mutated SLAC1 proteins revealed that in plants one of these SLAC1 residues is specifically required for the stomatal CO2 response, but not for ABA responses. These findings suggest that SLAC1 not only mediates anion efflux from guard cells, but also that SLAC1 could contribute as a CO2/HCO3- sensing in guard cells. These analyses suggest that SLAC1 can function as a “secondary” bicarbonate/CO2 sensor, but not as the primary CO2/bicarbonate sensor.

[CO2] elevation and the plant hormone abscisic acid (ABA) both trigger rapid stomatal closure via regulation of ion channels in guard cells. Abscisic acid is known to enhance CO2 responses. However, it has remained unknown whether [CO2]-triggered stomatal closure is directly mediated via activation of the early ABA synthesis and signal transduction pathway and how these pathways converge. To address these questions, stomatal CO2 responses were analyzed in ABA synthesis mutants and ABA receptor mutants. Experiments using higher order mutants show that abscisic acid synthesis and signaling components are essential for robust CO2 responses. Furthermore, direct biochemical and patch clamp analyses of guard cell CO2 and ABA signal transduction were pursued. Moreover, newly developed real-time ABA FRET nano-reporter expressing plants were generated to determine whether CO2 elevation causes rapid ABA concentration changes in guard cells. Taken together these interdisciplinary analyses provide strong evidence for a requirement of basal ABA signal transduction for CO2 signaling and point to a new and unexpected understanding of how CO2 signaling and ABA signaling merge downstream of early ABA and CO2 signaling mechanisms that both close stomata.

New findings on CO2 sensing mechanisms and on dissecting CO2-specific signaling in grasses will be presented. A model for early CO2 signal transduction mechanisms that control stomatal movements will be discussed.

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16:10-16:20 Discussion

16:20-16:50 The effects of carbon dioxide on pulmonary inflammatory processes arising from septic and aseptic aetiologies

Professor Daniel O'Toole, National University of Ireland, Galway, Ireland

Abstract

Acute respiratory distress syndrome (ARDS), a lung disease with rapid onset and high mortality, is characterised by inflammatory signalling pathway activation, infiltration of peripheral leukocytes into the pulmonary space and resultant systemic hypoxia and hypercapnia. Aetiology is typically pathogenic, but also arises due to factors including ventilator induced lung injury (VILI). Permissive or therapeutic hypercapnia are useful anti-inflammatory approaches to ARDS management, but molecular mechanisms are only slowly being revealed. In a series of experiments, rats were buffered renally or ventilated with 5% CO2 and received caecal puncture, E.coli instillation or increased volume ventilation. Assessment was through blood gas analysis, biochemical markers and lung tissue histology. In vitro, lung epithelial and other cells were exposed to increasing CO2 and subject to scratch wound, cytokine, endotoxin or cyclic mechanical stretch injury. Transfection and immunoprecipitation studies examined the influence of CO2 on various points along the NFκB signalling pathway. Hypercapnia attenuated systemic sepsis, though unbuffered alone reduced lung complications. CO2 related benefit was observed in both early and prolonged sepsis. VILI was attenuated by hypercapnia, reflected in a mechanical stretch model of lung epithelium. Hypercapnia diminished the NFκB inflammatory response in multiple cell lines independently of cytoplasmic pH, suggesting direct control by CO2. IKK2 enzymatic activity, IκBα degradation and NFκB translocation were all impaired, as was healing of epithelial scratch wounds, by elevated CO2. In conclusion, hypercapnia is anti-inflammatory in a range of pulmonary injury models, and is inhibitory across many points of the central NFκB inflammatory pathway.

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16:50-17:00 Discussion

17:00-18:00

Poster session and drinks reception

03 December

09:00-12:10

Session 3

8 talks Show detail Hide detail

Chairs

Dr Vicki Linthwaite, Durham University, UK

09:00-09:30 Hypercapnia in the critcally ill

Professor John Laffey, National University of Ireland, Galway, Ireland

Abstract

Arterial CO2 tensions (PaCO2) represents a balance between CO2 production and elimination via the lungs, and in health is maintained within a tight range (3.5 – 4.5 kPa). Traditional approaches to CO2 management in the critically ill emphasized the use of higher tidal and minute ventilation to avoid hypercapnia and its associated the risks. The demonstration that high lung stretch directly injures the lungs heralded the use of more protective ventilatory strategies that reduce lung stretch, and have been proven to improve survival in patients with ARDS. Consequently, hypercapnia – and its associated hypercapnic acidosis (HCA) - is prevalent in the critically ill, ‘permitted’ order to realize the benefits of lower lung stretch. Experimental and clinical investigations have generated key advances in our understanding of the effects of hypercapnia. Hypercapnia to be a potent biologic agent, with the potential to exert both beneficial and potentially harmful effects. Hypercapnia modulates the innate immune response, with inhibition of nuclear factor kappa-B, is a key transcriptional protein in injury, inflammation and repair, mediating diverse effects of hypercapnia. Advances in extracorporeal technologies have made possible the direct removal of CO2 while maintaining lung protective ventilation, a promising, though as yet unproven, approach. Consequently, it is important to understand the biology of hypercapnia, in order to best understand when hypercapnia should be encouraged, tolerated or avoided in patients with ARDS.

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09:30-09:40 Discussion

09:40-10:10 CO2 sensing in the brain

Professor Nicholas Dale, University of Warwick, UK

Abstract

The detection and regulated excretion of CO2, via breathing, is fundamental for homeostatic control of blood pH and preservation of life. Breathing is highly sensitive to the partial pressure of CO2 (PCO2) in blood. This vital physiological function was previously thought to depend exclusively upon the indirect changes in pH that follow the accumulation of CO2. However, evidence suggests that CO2 can have direct effects on breathing in addition to those of pH.

Connexins are large-conductance hexameric plasma membrane channels. They can dock together to form a passageway between adjacent cells, a gap junction, to permit transfer of ions and small molecules. Connexin channels not docked to those in neighbouring cells form “hemichannels” and open to the extracellular space. Chemosensory cells at the surface of the medulla oblongata use hemichannels of connexin26 (Cx26) to detect CO2 and effect adaptive changes in breathing. Physiological levels CO2 cause hemichannels of Cx26 to open, permitting the release of the neurotransmitter ATP and excitation of the neural networks controlling breathing. CO2 most likely binds to Cx26 by carbamylating Lys125, which forms a salt bridge to Arg104 on a neighbouring subunit to open the hemichannel.

Understanding the interaction of CO2 with Cx26 has enabled the rational design of a dominant negative subunit, dnCx26, which coassembles with wild type Cx26 to remove its CO2 sensitivity. Transduction with dnCx26 of the chemosensory cells in the medulla oblongata greatly reduces the chemosensitivity of breathing, thus directly linking the functional motif of CO2-binding to the physiological function of Cx26.

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10:10-10:20 Discussion

10:20-10:50 Coffee

10:50-11:20 CO2 diffusion inside leaves during photosynthesis

Dr Tory Clarke, Australian National University, Australia

Abstract

The rate of photosynthesis is very sensitive to the level of CO2 inside the chloroplasts, where photosynthesis takes place and CO2 is fixed by rubisco. CO2 first diffuses from the atmosphere through stomatal pores into the substomatal space. The CO2 must then cross internal airspace, cell walls, plasmalemma, cytoplasm, chloroplast envelope and part of the chloroplast stroma before it is fixed in the first step of the Calvin-Benson cycle. The combined conductance to CO2 transfer from substomatal cavities to the site of fixation is termed mesophyll conductance. In order to estimate mesophyll conductance, the exchange of CO2 from atmosphere into the leaf, together with the isotopic composition of the CO2 is measured. By exploiting Rubisco’s natural preference for 12CO2 over 13CO2, we can calculate mesophyll conductance from carbon isotopic discrimination. Mesophyll conductance is an important photosynthetic parameter that influences the amount of CO2 available for fixation and is a target for improving crop productivity. Understanding variations in mesophyll conductance across leaves, and what drives these changes, is essential for modelling how the manipulation of photosynthetic pathways may alter plant productivity. Using Nicotiana tabacum var. Samsun, we have investigated how mesophyll conductance, and other photosynthetic and leaf anatomy parameters, vary across leaf ages and throughout the canopy, with the goal of better informing plant productivity models.

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11:20-11:30 Discussion

11:30-12:00 Molecular and cellular mechanisms for CO2 sensing: lessons from aquatic organisms

Dr Martin Tresguerres, Scripps Institution of Oceanography, UC San Diego, USA

Abstract

My laboratory uses aquatic animals as models to study the evolution of acid-base sensing mechanisms at the molecular, cellular, and organismal levels. Because the internal fluids of aquatic organisms have lower CO2 and HCO3- levels and higher pH (“acid-base” parameters) compared to air-breathing vertebrates, their underlying acid-base sensing mechanisms must be tuned to different and specific set points. Kinetic assays on the evolutionary conserved acid-sensing enzyme soluble adenylyl cyclase (sAC) demonstrate a species-specific responsiveness to [HCO3-] that in each case matches physiologically relevant levels. For example, sAC’s HCO3- half-maximal stimulation is ~5 mM in sharks, ~10 mM in bony fishes and coral, which are lower than the ~20 mM reported in mammals. Additionally, aquatic animals routinely experience metabolic and environmental acid-base disturbances that can span >1 pH unit and >10-fold changes in [HCO3-]. Physiologically, this implies acid-base sensing plays essential and multiple homeostatic roles. Experimentally, this is advantageous because it allows imposing extreme (but physiologically relevant) acid-base challenges (i.e. 0-100 mM bicarbonate, pH 6.0-9.0) that maximize the magnitude of physiological responses and facilitate their detection. These approaches have led to the discovery of several novel physiological functions under sAC modulation in aquatic animals, including base secretion in shark gill epithelial cells, salt and fluid absorption across fish intestine, heart beat rate in hagfish, and pHi regulation in corals. In addition to their implications for organismal, environmental, and evolutionary physiology, these results provide clues about similar processes that might be under sAC control in humans and therefore might have biomedical relevance.

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12:00-12:10 Discussion

12:10-13:20

Lunch

13:20-17:00

Session 4

9 talks Show detail Hide detail

Chairs

Professor Martin Cann, Durham University, UK

13:20-13:50 Hypercapnia and suppression of lung host defense

Professor Peter Sporn, Northwestern University, USA

Abstract

Hypercapnia, or elevated PCO2 in blood and tissue, is an independent risk factor for mortality in patients with severe acute and advanced chronic lung disease. Bacterial and viral lung infections are often proximate events leading to poor clinical outcomes in such individuals. The Sporn group showed that exposure to elevated concentrations of CO2 inhibits innate immune gene expression and phagocytosis in macrophages, suggesting a causal role for hypercapnia in worse outcomes related to lung infection. Further, Sporn and colleagues showed that normoxic hypercapnia increased the mortality of bacterial pneumonia in mice. In addition, hypercapnia suppressed macrophage antiviral gene expression and increased the mortality of influenza A (IAV) infection in mice. Interestingly, hypercapnia also inhibited innate immune gene expression and increased the mortality of bacterial infection in Drosophila. A genome-wide RNAi screen then led to the identification of a transcription factor, zfh2, whose expression was required for CO2-induced immunosuppression in the fly in vitro and in vivo. The Sporn group generated a myeloid-specific mouse knockout of Zfhx3, the mammalian ortholog of zfh2, and finds that Zfhx3-deficient macrophages from the mutant are protected against hypercapnia-induced suppression of antiviral gene expression and increased growth of IAV in vitro. Further, the myeloid Zfhx3-deficient mouse is partially protected against IAV-induced lung injury. RNA-seq analysis of alveolar macrophages from IAV-infected mice reveals that host defense-related gene expression pathways downregulated by hypercapnia in the wild-type are upregulated in alveolar macrophages from Zfhx3-deficient mice. Future studies will further elucidate the molecular mechanism(s) by which hypercapnia suppresses lung host defense.

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13:50-14:00 Discussion

14:00-14:30 Carbon dioxide and hypercapnia in ventilation/perfusion regulation and inflammation

Professor Erik Swenson, University of Washington, USA

Abstract

There has traditionally been a far greater emphasis in respiratory physiology and medicine on effects and roles of O2 than CO2 on the lung. This ‘oxycentric’ focus has relegated CO2 to that of the neglected step sister of the two gases, yet it has considerable influence on gas exchange efficiency and inflammation that are quite under-recognized.  When either regional ventilation (VA) or perfusion (Q) varies, both O2 and CO2-dependent mechanisms are evoked to restore the balance of local blood flow and local gas flow. Matching of Q to changes in VA is accomplished by both hypoxic pulmonary vasoconstriction (HPV) and hypercapnic pulmonary vasoconstriction (HCPV), acting equally to limit perfusion into poorly ventilated areas. HCPV may be more important since it is active over the entire range of PCO2 in normal and diseased lungs, whereas as HPV is only engaged below a PO2 of 60 mmHg. In contrast to perfusion regulation, regulation of regional ventilation has no dependence on PO2. The changes in alveolar PCO2 caused by changes in Q act to alter VA by actions at the bronchial level by hypercapnic bronchodilation and at the parenchymal level by hypercapnic pneumo-relaxation causing changes in tissue compliance. These CO2-mediated effects are largely the result of the accompanying pH change which is accelerated by carbonic anhydrase in the lung. Beyond the benefits of CO2 on gas exchange efficiency and VA/Q matching, it also has anti-inflammatory effects that have the potential to mitigate lung injury from ischemia-reperfusion damage, acute respiratory distress syndrome and infections. 

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14:30-14:40 Discussion

14:40-15:10 Tea

15:10-15:40 Stomatal CO2 detection

Professor Julie Gray, Sheffield University, UK

Abstract

Applying either elevated atmospheric carbon dioxide concentrations or the drought hormone abscisic acid (ABA), to plant leaves brings about similar effects; they reduce the apertures of stomatal pores and reduce the number of stomata that form. These two stomatal responses allow plants to reduce their rate of transpiration and to conserve water. We therefore investigated whether the same signalling components might regulate stomatal responses to both [CO2] and ABA. Our results indicate that the stomatal [CO2] responses utilise components of the ABA signaling pathway including ABA biosynthesis and ABA receptors. Thus it appears possible that stomatal [CO2] responses are mediated by the ABA response pathway. However, we found no evidence for an increase in leaf ABA levels in response to elevated [CO2], suggesting that ABA either increases the sensitivity of the system to [CO2], or that any [CO2]-induced increase in ABA occurs specifically in the stomata. 

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15:40-15:50 Discussion

15:50-16:20 CO2 and mammalian innate immunity

Dr Eoin Cummins, University College Dublin, Ireland

Abstract

Carbon dioxide (CO2) is a product of aerobic metabolism that is mainly exhaled via the lungs to maintain stable paCO2 pressure (normocapnia) and blood pH. Hypercapnia (paCO2 >50mmHg) is a feature of chronic lung diseases, and permissive hypercapnia occurs in the intensive care setting as a feature of a protective ventilation strategy. Several in vitro and in vivo animal based studies have implicated CO2-dependent signaling in the suppression of immune and inflammatory signaling. Thus, these CO2-dependent signaling events may be detrimental in the context of a bacterial infection but of benefit in the context of uncontrolled inflammation. However, the molecular mechanisms underpinning CO2-dependent changes in gene expression are not well understood and are the focus of research in the Cummins lab. This presentation will initially outline investigations from the lab into how elevated CO2 modulates signaling, particularly within the NFkB pathway. Hypercapnia causes a marked change in the nuclear localisation and processing of key NFkB family members and modulates the expression of NFkB target genes. Dr Cummins will outline some of the recent RNA-seq and proteomic approaches taken by the group to understand the molecular mechanisms underpinning CO2-dependent regulation of inflammatory signaling. Finally, hypoxia and hypercapnia frequently co-exist given that O2 and CO2 are the substrate and product of aerobic metabolism respectively. Dr Cummins will describe important cross-talk between the O2 and CO2-sensing pathways and demonstrate that hypercapnia suppresses the cellular adaptive response to low oxygen in vitro and in vivo.

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16:20-16:30 Discussion

16:30-17:00 Closing discussion

Carbon dioxide detection in biological systems Theo Murphy international scientific meeting organised by Professor Martin Cann, Dr Vicki Linthwaite and Dr Eoin Cummins. Kavli Royal Society Centre, Chicheley Hall Newport Pagnell Buckinghamshire MK16 9JJ
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