Lyn is a redox sensor that mediates leukocyte wound attraction in vivo

ROS regulation of microdomain Ca(2+) signalling at the dyads

Reactive oxygen species (ROS) are emerging as centre-stage players in cardiac functional regulation. ROS and Ca(2+) signals converge at dyads, the structural and functional units of cardiac excitation-contraction coupling. These two prominent signalling systems are intertwined with ROS modulation of the entire Ca(2+)-signalling network, and vice versa. While constitutively generated homoeostatic ROS are important in setting the redox potential of the intracellular milieu, dynamic signalling ROS shape microdomain and global Ca(2+) signals on both the beat-to-beat and greater time scales. However, ROS effects are complex and subtle, characterized by multiphasic and bidirectional Ca(2+) responses; and sustained oxidative stress may lead to compromised contractility and arrhythmogenicity. These new understandings should be leveraged to harness ROS for their beneficial roles while avoiding deleterious effects in the heart.

The role of transcription-independent damage signals in the initiation of epithelial wound healing

Wound healing is an essential biological process that comprises sequential steps aimed at restoring the architecture and function of damaged cells and tissues. This process begins with conserved damage signals, such as Ca(2+), hydrogen peroxide (H2O2) and ATP, that diffuse through epithelial tissues and initiate immediate gene transcription-independent cellular effects, including cell shape changes, the formation of functional actomyosin structures and the recruitment of immune cells. These events integrate the ensuing transcription of specific wound response genes that further advance the wound healing response. The immediate importance of transcription-independent damage signals illustrates that healing a wound begins as soon as damage occurs.

Amputation-induced reactive oxygen species are required for successful Xenopus tadpole tail regeneration

Understanding the molecular mechanisms that promote successful tissue regeneration is critical for continued advancements in regenerative medicine. Vertebrate amphibian tadpoles of the species Xenopus laevis and Xenopus tropicalis have remarkable abilities to regenerate their tails following amputation, through the coordinated activity of numerous growth factor signalling pathways, including the Wnt, Fgf, Bmp, Notch and TGF-β pathways. Little is known, however, about the events that act upstream of these signalling pathways following injury. Here, we show that Xenopus tadpole tail amputation induces a sustained production of reactive oxygen species (ROS) during tail regeneration. Lowering ROS levels, using pharmacological or genetic approaches, reduces the level of cell proliferation and impairs tail regeneration. Genetic rescue experiments restored both ROS production and the initiation of the regenerative response. Sustained increased ROS levels are required for Wnt/β-catenin signalling and the activation of one of its main downstream targets, fgf20 (ref. 7), which, in turn, is essential for proper tail regeneration. These findings demonstrate that injury-induced ROS production is an important regulator of tissue regeneration.

ATP-mediated transactivation of the epidermal growth factor receptor in airway epithelial cells involves DUOX1-dependent oxidation of Src and ADAM17

The respiratory epithelium is subject to continuous environmental stress and its responses to injury or infection are largely mediated by transactivation of the epidermal growth factor receptor (EGFR) and downstream signaling cascades. Based on previous studies indicating involvement of ATP-dependent activation of the NADPH oxidase homolog DUOX1 in epithelial wound responses, the present studies were performed to elucidate the mechanisms by which DUOX1-derived H₂O₂ participates in ATP-dependent redox signaling and EGFR transactivation. ATP-mediated EGFR transactivation in airway epithelial cells was found to involve purinergic P2Y₂ receptor stimulation, and both ligand-dependent mechanisms as well as ligand-independent EGFR activation by the non-receptor tyrosine kinase Src. Activation of Src was also essential for ATP-dependent activation of the sheddase ADAM17, which is responsible for liberation and activation of EGFR ligands. Activation of P2Y₂R results in recruitment of Src and DUOX1 into a signaling complex, and transient siRNA silencing or stable shRNA transfection established a critical role for DUOX1 in ATP-dependent activation of Src, ADAM17, EGFR, and downstream wound responses. Using thiol-specific biotin labeling strategies, we determined that ATP-dependent EGFR transactivation was associated with DUOX1-dependent oxidation of cysteine residues within Src as well as ADAM17. In aggregate, our findings demonstrate that DUOX1 plays a central role in overall epithelial defense responses to infection or injury, by mediating oxidative activation of Src and ADAM17 in response to ATP-dependent P2Y₂R activation as a proximal step in EGFR transactivation and downstream signaling.

Peroxiredoxins and sulfiredoxin at the crossroads of the NO and H2O2 signaling pathways

Peroxiredoxins (Prxs) are a family of peroxidases that maintain thiol homeostasis by catalyzing the reduction of organic hydroperoxides, H2O2, and peroxynitrite. Eukaryotic 2-Cys-Prxs, also referred to as typical Prxs, can be inactivated by oxidation of the catalytic cysteine to sulfinic acid, which may regulate the intracellular messenger function of H2O2. A small redox protein, sulfiredoxin (Srx), has been shown to reduce sulfinylated 2-Cys-Prxs and thus to regenerate active 2-Cys-Prxs. We previously reported that cytokine-induced nitric oxide (NO) intervenes in this pathway by decreasing the level of 2-Cys overoxidation and by upregulating Srx through the activation of the transcription factor nuclear factor erythroid 2-related factor (Nrf2). Here, we describe the methods used to monitor the interplay between NO and H2O2 in the regulation of the Prx/Srx system in immunostimulated macrophages, which produce both reactive oxygen species and NO.

Dual oxidase-1 is required for airway epithelial cell migration and bronchiolar reepithelialization after injury

The respiratory epithelium plays a critical role in innate defenses against airborne pathogens and pollutants, and alterations in epithelial homeostasis and repair mechanisms are thought to contribute to chronic lung diseases associated with airway remodeling. Previous studies implicated the nicotinamide adenine dinucleotide phosphate-reduced oxidase dual oxidase-1 (DUOX1) in redox signaling pathways involved in in vitro epithelial wound responses to infection and injury. However, the importance of epithelial DUOX1 in in vivo epithelial repair pathways has not been established. Using small interfering (si)RNA silencing of DUOX1 expression, we show the critical importance of DUOX1 in wound responses in murine tracheal epithelial (MTE) cells in vitro, as well as its contribution to epithelial regeneration in vivo in a murine model of epithelial injury induced by naphthalene, a selective toxicant of nonciliated respiratory epithelial cells (club cells [Clara]). Whereas naphthalene-induced club-cell injury is normally followed by epithelial regeneration after 7 and 14 days, such airway reepithelialization was significantly delayed after the silencing of airway DUOX1 by oropharyngeal administration of DUOX1-targeted siRNA. Wound closure in MTE cells was related to DUOX1-dependent activation of the epidermal growth factor receptor (EGFR) and the transcription factor signal transducer and activator of transcription-3 (STAT3), known mediators of epithelial cell migration and wound responses. Moreover, in vivo DUOX1 silencing significantly suppressed naphthalene-induced activation of STAT3 and EGFR during early stages of epithelial repair. In conclusion, these experiments demonstrate for the first time an important function for epithelial DUOX1 in lung epithelial regeneration in vivo, by promoting EGFR-STAT3 signaling and cell migration as critical events in initial repair.

Inflammatory chemokines direct and restrict leukocyte migration within live tissues as glycan-bound gradients

Chemokines are essential in many cell migration processes, including the recruitment of leukocytes to sites of infection. In the latter context, chemokines promote leukocyte extravasation into the relevant tissue through a well-studied cascade of events. It is widely believed that chemokines further guide leukocytes within tissues via chemotaxis, the directed migration along gradients of soluble ligands. However, the basic mechanism of chemokine action within tissues has yet to be formally addressed in vivo. We identified a chemokine (zCxcl8) that recruits zebrafish neutrophils to infection loci and analyzed its function directly within interstitial tissues of living larvae. Using noninvasive imaging and a controlled cellular source of zCxcl8, we found that zCxcl8 guides neutrophils in a 2-fold manner: by biasing cell speed according to direction (orthotaxis) and by restricting cell motility near the source. We further show that zCxcl8 establishes tissue-bound gradients in vivo by binding to heparan sulfate proteoglycans (HSPGs). Inhibition of this interaction compromised both directional guidance and restriction of neutrophil motility. Thus, by interacting with extracellular HSPGs, chemokines establish robust surface-bound (haptotactic) gradients that mediate both recruitment and retention of leukocytes at sites of infection.

Effects of hydrogen peroxide on wound healing in mice in relation to oxidative damage

It has been established that low concentrations of hydrogen peroxide (H₂O₂) are produced in wounds and is required for optimal healing. Yet at the same time, there is evidence that excessive oxidative damage is correlated with poor-healing wounds. In this paper, we seek to determine whether topical application of H₂O₂ can modulate wound healing and if its effects are related to oxidative damage. Using a C57BL/6 mice excision wound model, H₂O₂ was found to enhance angiogenesis and wound closure at 10 mM but retarded wound closure at 166 mM. The delay in closure was also associated with decreased connective tissue formation, increased MMP-8 and persistent neutrophil infiltration. Wounding was found to increase oxidative lipid damage, as measured by F₂-isoprostanes, and nitrative protein damage, as measured by 3-nitrotyrosine. However H₂O₂ treatment did not significantly increase oxidative and nitrative damage even at concentrations that delay wound healing. Hence the detrimental effects of H₂O₂ may not involve oxidative damage to the target molecules studied.

The role of Src kinase in macrophage-mediated inflammatory responses

Src kinase (Src) is a tyrosine protein kinase that regulates cellular metabolism, survival, and proliferation. Many studies have shown that Src plays multiple roles in macrophage-mediated innate immunity, such as phagocytosis, the production of inflammatory cytokines/mediators, and the induction of cellular migration, which strongly implies that Src plays a pivotal role in the functional activation of macrophages. Macrophages are involved in a variety of immune responses and in inflammatory diseases including rheumatoid arthritis, atherosclerosis, diabetes, obesity, cancer, and osteoporosis. Previous studies have suggested roles for Src in macrophage-mediated inflammatory responses; however, recently, new functions for Src have been reported, implying that Src functions in macrophage-mediated inflammatory responses that have not been described. In this paper, we discuss recent studies regarding a number of these newly defined functions of Src in macrophage-mediated inflammatory responses. Moreover, we discuss the feasibility of Src as a target for the development of new pharmaceutical drugs to treat macrophage-mediated inflammatory diseases. We provide insights into recent reports regarding new functions for Src that are related to macrophage-related inflammatory responses and the development of novel Src inhibitors with strong immunosuppressive and anti-inflammatory properties, which could be applied to various macrophage-mediated inflammatory diseases.

Fyn regeneration

A Src family kinase and several other signaling pathways help repair zebrafish fins after wounding.

Early redox, Src family kinase, and calcium signaling integrate wound responses and tissue regeneration in zebrafish

Redox, SFK, and calcium signaling are immediate “wound signals” that integrate early wound responses and late epimorphic regeneration.

Tissue injury can lead to scar formation or tissue regeneration. How regenerative animals sense initial tissue injury and transform wound signals into regenerative growth is an unresolved question. Previously, we found that the Src family kinase (SFK) Lyn functions as a redox sensor in leukocytes that detects H₂O₂ at wounds in zebrafish larvae. In this paper, using zebrafish larval tail fins as a model, we find that wounding rapidly activated SFK and calcium signaling in epithelia. The immediate SFK and calcium signaling in epithelia was important for late epimorphic regeneration of amputated fins. Wound-induced activation of SFKs in epithelia was dependent on injury-generated H₂O₂. A SFK member, Fynb, was responsible for fin regeneration. This work provides a new link between early wound responses and late regeneration and suggests that redox, SFK, and calcium signaling are immediate “wound signals” that integrate early wound responses and late epimorphic regeneration.

Emerging applications for zebrafish as a model organism to study oxidative mechanisms and their roles in inflammation and vascular accumulation of oxidized lipids

With the advent of genetic engineering, zebrafish (Danio rerio) were recognized as an attractive model organism to study many biological processes. Remarkably, the small size and optical transparency of zebrafish larvae enable high-resolution imaging of live animals. Zebrafish respond to various environmental and pathological factors with robust oxidative stress. In this article, we provide an overview of the molecular mechanisms involved in oxidative stress and antioxidant response in zebrafish. Existing applications of genetically encoded fluorescent sensors allow imaging, in real time, of the production of H(2)O(2) and studying its involvement in inflammatory responses, as well as activation of the oxidation-sensitive transcription factors HIF and NRF2. Oxidative stress, combined with hyperlipidemia, leads to oxidation of lipoproteins, the process that contributes significantly to the development of atherosclerosis in humans. Recent work found that feeding zebrafish a high-cholesterol diet results in hypercholesterolemia, vascular lipid accumulation, and extreme lipoprotein oxidation. Generation of a transgenic zebrafish expressing a green fluorescent protein-tagged human antibody to malondialdehyde (MDA)-modified LDL makes possible the in vivo visualization of MDA epitopes in the vascular wall and testing of the efficacy of antioxidants and dietary interventions. Thus, using zebrafish as a model organism provides important advantages in studying the roles of reactive oxygen species and lipid oxidation in basic biologic and pathologic processes.

The role of microtubules in neutrophil polarity and migration in live zebrafish

Microtubules control cell motility by positively regulating polarization in many cell types. However, how microtubules regulate leukocyte migration is not well understood, particularly in living organisms. Here we exploited the zebrafish system to study the role of microtubules in neutrophil migration in vivo. The localization of microtubules was visualized in motile neutrophils using various bioprobes, revealing that, in contrast to what has been seen in studies in vitro, the microtubule organizing center is positioned in front of the nucleus (relative to the direction of migration) in motile neutrophils. Microtubule disassembly impaired attraction of neutrophils to wounds but enhanced the polarity of F-actin dynamics as measured by the distribution of stable and dynamic F-actin. Microtubule depolymerization inhibited polarized phosphoinositol 3-kinase (PI(3)K) activation at the leading edge and induced rapid PI(3)K independent motility. Finally, we show that microtubules exert their effects on neutrophil polarity and motility at least in part by the negative regulation of both Rho and Rac activity. These results provide new insight into the role of microtubules in neutrophil migration in a living vertebrate and show that the motility of these professional migratory cells are subject to distinctly different rules from those established for other cell types.

The SH2-domain-containing inositol 5-phosphatase (SHIP) limits the motility of neutrophils and their recruitment to wounds in zebrafish

Neutrophil recruitment to sites of injury or infection is essential for host defense, but it needs to be tightly regulated to prevent tissue damage. Phosphoinositide 3-kinase (PI3K), which generates the phosphatidylinositol (3,4,5)-trisphosphate [PI(3,4,5)P(3)], is necessary for neutrophil motility in vivo; however, the role of SH2-domain-containing 5-inositol phosphatase (SHIP) enzymes, which hydrolyze PI(3,4,5)P(3) to phosphatidylinositol 3,4-bisphosphate [PI(3,4)P(2)], is not well understood. Here we show that SHIP phosphatases limit neutrophil motility in live zebrafish. Using real-time imaging of bioprobes specific for PI(3,4,5)P(3) and PI(3,4)P(2) in neutrophils, we found that PI(3,4,5)P(3) and PI(3,4)P(2) accumulate at the leading edge while PI(3,4)P(2) also localizes to the trailing edge of migrating neutrophils in vivo. Depletion of SHIP phosphatases using morpholino oligonucleotides led to increased neutrophil 3D motility and neutrophil infiltration into wounds. The increase in neutrophil wound recruitment in SHIP morphants was rescued by treatment with low dose PI3Kγ inhibitor, suggesting that SHIP limits neutrophil motility by modulating PI3K signaling. Moreover, overexpression of the SHIP phosphatase domain in neutrophils impaired neutrophil 3D migration. Taken together, our findings suggest that SHIP phosphatases control neutrophil inflammation by limiting neutrophil motility in vivo.

Neutrophil-delivered myeloperoxidase dampens the hydrogen peroxide burst after tissue wounding in zebrafish

Prompt neutrophil arrival is critical for host defense immediately after injury [1-3]. Following wounding, a hydrogen peroxide (H(2)O(2)) burst generated in injured tissues is the earliest known leukocyte chemoattractant [4]. Generating this tissue-scale H(2)O(2) gradient uses dual oxidase [4] and neutrophils sense H(2)O(2) by a mechanism involving the LYN Src-family kinase [5], but the molecular mechanisms responsible for H(2)O(2) clearance are unknown [6]. Neutrophils carry abundant amounts of myeloperoxidase, an enzyme catalyzing an H(2)O(2)-consuming reaction [7, 8]. We hypothesized that this neutrophil-delivered myeloperoxidase downregulates the high tissue H(2)O(2) concentrations that follow wounding. This was tested in zebrafish using simultaneous fluorophore-based imaging of H(2)O(2) concentrations and leukocytes [4, 9-11] and a new neutrophil-replete but myeloperoxidase-deficient mutant (durif). Leukocyte-depleted zebrafish had an abnormally sustained wound H(2)O(2) burst, indicating that leukocytes themselves were required for H(2)O(2) downregulation. Myeloperoxidase-deficient zebrafish also had abnormally sustained high wound H(2)O(2) concentrations despite similar numbers of arriving neutrophils. A local H(2)O(2)/myeloperoxidase interaction within wound-recruited neutrophils was demonstrated. These data demonstrate that leukocyte-delivered myeloperoxidase cell-autonomously downregulates tissue-generated wound H(2)O(2) gradients in vivo, defining a new requirement for myeloperoxidase during inflammation. Durif provides a new animal model of myeloperoxidase deficiency closely phenocopying the prevalent human disorder [7, 12, 13], offering unique possibilities for investigating its clinical consequences.

Chemokine-dependent T cell migration requires aquaporin-3-mediated hydrogen peroxide uptake

The water/glycerol channel aquaporin-3 is required for chemokine-dependent T cell migration during immune responses.

Chemokine-dependent trafficking is indispensable for the effector function of antigen-experienced T cells during immune responses. In this study, we report that the water/glycerol channel aquaporin-3 (AQP3) is expressed on T cells and regulates their trafficking in cutaneous immune reactions. T cell migration toward chemokines is dependent on AQP3-mediated hydrogen peroxide (H₂O₂) uptake but not the canonical water/glycerol transport. AQP3-mediated H₂O₂ transport is essential for the activation of the Rho family GTPase Cdc42 and the subsequent actin dynamics. Coincidentally, AQP3-deficient mice are defective in the development of hapten-induced contact hypersensitivity, which is attributed to the impaired trafficking of antigen-primed T cells to the hapten-challenged skin. We therefore suggest that AQP3-mediated H₂O₂ uptake is required for chemokine-dependent T cell migration in sufficient immune response.

Reactive oxygen species regulate protrusion efficiency by controlling actin dynamics

Productive protrusions allowing motile cells to sense and migrate toward a chemotactic gradient of reactive oxygen species (ROS) require a tight control of the actin cytoskeleton. However, the mechanisms of how ROS affect cell protrusion and actin dynamics are not well elucidated yet. We show here that ROS induce the formation of a persistent protrusion. In migrating epithelial cells, protrusion of the leading edge requires the precise regulation of the lamellipodium and lamella F-actin networks. Using fluorescent speckle microscopy, we showed that, upon ROS stimulation, the F-actin retrograde flow is enhanced in the lamellipodium. This event coincides with an increase of cofilin activity, free barbed ends formation, Arp2/3 recruitment, and ERK activity at the cell edge. In addition, we observed an acceleration of the F-actin flow in the lamella of ROS-stimulated cells, which correlates with an enhancement of the cell contractility. Thus, this study demonstrates that ROS modulate both the lamellipodium and the lamella networks to control protrusion efficiency.

Spatiotemporal regulation of Src and its substrates at invadosomes

In the past decade, substantial progress has been made in understanding how Src family kinases regulate the formation and function of invadosomes. Invadosomes are organized actin-rich structures that contain an F-actin core surrounded by an adhesive ring and mediate invasive migration. Src kinases orchestrate, either directly or indirectly, each phase of the invadosome life cycle including invadosome assembly, maturation and matrix degradation and disassembly. Complex arrays of Src effector proteins are involved at different stages of invadosome maturation and their spatiotemporal activity must be tightly regulated to achieve effective invasive migration. In this review, we highlight some recent progress and the challenges of understanding how Src is regulated temporally and spatially to orchestrate the dynamics of invadosomes and mediate cell invasion.

Neutrophil reverse migration becomes transparent with zebrafish

The precise control of neutrophil-mediated inflammation is critical for both host defense and the prevention of immunopathology. In vivo imaging studies in zebrafish, and more recently in mice, have made the novel observation that neutrophils leave a site of inflammation through a process called neutrophil reverse migration. The application of advanced imaging techniques to the genetically tractable, optically transparent zebrafish larvae was critical for these advances. Still, the mechanisms underlying neutrophil reverse migration and its effects on the resolution or priming of immune responses remain unclear. Here, we review the current knowledge of neutrophil reverse migration, its potential roles in host immunity, and the live imaging tools that make zebrafish a valuable model for increasing our knowledge of neutrophil behavior in vivo.

Pathogen recognition and activation of the innate immune response in zebrafish

The zebrafish has proven itself as an excellent model to study vertebrate innate immunity. It presents us with possibilities for in vivo imaging of host-pathogen interactions which are unparalleled in mammalian model systems. In addition, its suitability for genetic approaches is providing new insights on the mechanisms underlying the innate immune response. Here, we review the pattern recognition receptors that identify invading microbes, as well as the innate immune effector mechanisms that they activate in zebrafish embryos. We compare the current knowledge about these processes in mammalian models and zebrafish and discuss recent studies using zebrafish infection models that have advanced our general understanding of the innate immune system. Furthermore, we use transcriptome analysis of zebrafish infected with E. tarda, S. typhimurium, and M. marinum to visualize the gene expression profiles resulting from these infections. Our data illustrate that the two acute disease-causing pathogens, E. tarda and S. typhimurium, elicit a highly similar proinflammatory gene induction profile, while the chronic disease-causing pathogen, M. marinum, induces a weaker and delayed innate immune response.

Hydrogen peroxide in inflammation: messenger, guide, and assassin

Starting as a model for developmental genetics, embryology, and organogenesis, the zebrafish has become increasingly popular as a model organism for numerous areas of biology and biomedicine over the last decades. Within haematology, this includes studies on blood cell development and function and the intricate regulatory mechanisms within vertebrate immunity. Here, we review recent studies on the immediate mechanisms mounting an inflammatory response by in vivo analyses using the zebrafish. These recently revealed novel roles of the reactive oxygen species hydrogen peroxide that have changed our view on the initiation of a granulocytic inflammatory response.

Distinct signalling mechanisms mediate neutrophil attraction to bacterial infection and tissue injury

The signals that guide neutrophils to sites of tissue injury or infection remain elusive. H(2)O(2) has been implicated in neutrophil sensing of tissue injury and transformed cells; however, its role in neutrophil recruitment to infection has not been explored. Here, using a pharmacological inhibitor of NADPH oxidases, diphenyleneiodonium (DPI), and genetic depletion of an epithelial-specific NADPH oxidase, we show that H(2)O(2) is not required for neutrophil detection of localized infection with the Gram-negative bacterium Pseudomonas aeruginosa. In contrast, PI3K signalling is required for neutrophil responses to both wounding and infection. In vivo imaging using a H(2)O(2) probe detects dynamic H(2)O(2) generation at wounds but not at infected tissue. Moreover, DPI no longer inhibits neutrophil wound attraction when P. aeruginosa is present in the media. Finally, DPI also fails to inhibit neutrophil recruitment to localized infection with the Gram-positive bacterium, Streptococcus iniae. Our findings demonstrate that different signals are involved in sensitizing neutrophils to pathogen versus non-pathogen induced tissue damage, providing a potential target to preferentially suppress non-specific immune damage without affecting the response to infection.