title: Mechanisms underlying the exquisite sensitivity of Candida albicans to combinatorial cationic and oxidative stress that enhances the potent fungicidal activity of phagocytes.
abstract: Immune cells exploit reactive oxygen species (ROS) and cationic fluxes to kill microbial pathogens, such as the fungus Candida albicans. Yet, C. albicans is resistant to these stresses in vitro. Therefore, what accounts for the potent antifungal activity of neutrophils? We show that simultaneous exposure to oxidative and cationic stresses is much more potent than the individual stresses themselves and that this combinatorial stress kills C. albicans synergistically in vitro. We also show that the high fungicidal activity of human neutrophils is dependent on the combinatorial effects of the oxidative burst and cationic fluxes, as their pharmacological attenuation with apocynin or glibenclamide reduced phagocytic potency to a similar extent. The mechanistic basis for the extreme potency of combinatorial cationic plus oxidative stress--a phenomenon we term stress pathway interference--lies with the inhibition of hydrogen peroxide detoxification by the cations. In C. albicans this causes the intracellular accumulation of ROS, the inhibition of Cap1 (a transcriptional activator that normally drives the transcriptional response to oxidative stress), and altered readouts of the stress-activated protein kinase Hog1. This leads to a loss of oxidative and cationic stress transcriptional outputs, a precipitous collapse in stress adaptation, and cell death. This stress pathway interference can be suppressed by ectopic catalase (Cat1) expression, which inhibits the intracellular accumulation of ROS and the synergistic killing of C. albicans cells by combinatorial cationic plus oxidative stress. Stress pathway interference represents a powerful fungicidal mechanism employed by the host that suggests novel approaches to potentiate antifungal therapy. Importance: The immune system combats infection via phagocytic cells that recognize and kill pathogenic microbes. Human neutrophils combat Candida infections by killing this fungus with a potent mix of chemicals that includes reactive oxygen species (ROS) and cations. Yet, Candida albicans is relatively resistant to these stresses in vitro. We show that it is the combination of oxidative plus cationic stresses that kills yeasts so effectively, and we define the molecular mechanisms that underlie this potency. Cations inhibit catalase. This leads to the accumulation of intracellular ROS and inhibits the transcription factor Cap1, which is critical for the oxidative stress response in C. albicans. This triggers a dramatic collapse in fungal stress adaptation and cell death. Blocking either the oxidative burst or cationic fluxes in human neutrophils significantly reduces their ability to kill this fungal pathogen, indicating that combinatorial stress is pivotal to immune surveillance.
authors.affiliation: School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom.
authors.forename: Despoina
authors.initials: D
authors.lastname: Kaloriti
authors.affiliation: School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom.
authors.forename: Mette
authors.initials: M
authors.lastname: Jacobsen
authors.affiliation: School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom.
authors.forename: Zhikang
authors.initials: Z
authors.lastname: Yin
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Miranda
authors.initials: M
authors.lastname: Patterson
authors.affiliation: School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom.
authors.forename: Anna
authors.initials: A
authors.lastname: Tillmann
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Smith
authors.affiliation: Department of Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom.
authors.forename: Emily
authors.initials: E
authors.lastname: Cook
authors.affiliation: Institute for Complex Systems and Mathematical Biology, King's College, University of Aberdeen, Old Aberdeen, Aberdeen, United Kingdom.
authors.forename: Tao
authors.initials: T
authors.lastname: You
authors.affiliation: Department of Medicine, Roswell Park Cancer Institute, Buffalo, New York, USA.
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Grimm
authors.affiliation: School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom.
authors.forename: Iryna
authors.initials: I
authors.lastname: Bohovych
authors.affiliation: Institute for Complex Systems and Mathematical Biology, King's College, University of Aberdeen, Old Aberdeen, Aberdeen, United Kingdom.
authors.forename: Celso
authors.initials: C
authors.lastname: Grebogi
authors.forename: Brahm H
authors.initials: BH
authors.lastname: Segal
authors.affiliation: School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom.
authors.forename: Neil A R
authors.initials: NA
authors.lastname: Gow
authors.affiliation: Department of Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom.
authors.forename: Ken
authors.initials: K
authors.lastname: Haynes
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
authors.forename: Janet
authors.initials: J
authors.lastname: Quinn
authors.affiliation: School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom al.brown@abdn.ac.uk.
authors.forename: Alistair J P
authors.initials: AJ
authors.lastname: Brown
mesh_terms: D000098:Acetophenones / Q000494:pharmacology; D002176:Candida albicans / Q000187:drug effects / Q000378:metabolism*; D005905:Glyburide / Q000494:pharmacology; D006801:Humans; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D010586:Phagocytes / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D000098:Acetophenones; C056165:acetovanillone; D005905:Glyburide