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

Wound healing across the animal kingdom: Crosstalk between the immune system and the extracellular matrix

Tissue regeneration is widespread in the animal kingdom. To date, key roles for different molecular and cellular programs in regeneration have been described, but the ultimate blueprint for this talent remains elusive. In animals capable of tissue regeneration, one of the most crucial stages is wound healing, whose main goal is to close the wound and prevent infection. In this stage, it is necessary to avoid scar formation to facilitate the activation of the immune system and remodeling of the extracellular matrix, key factors in promoting tissue regeneration. In this review, we will discuss the current state of knowledge regarding the role of the immune system and the interplay with the extracellular matrix to trigger a regenerative response.

Genetically Encoded Tools for Research of Cell Signaling and Metabolism under Brain Hypoxia

Hypoxia is characterized by low oxygen content in the tissues. The central nervous system (CNS) is highly vulnerable to a lack of oxygen. Prolonged hypoxia leads to the death of brain cells, which underlies the development of many pathological conditions. Despite the relevance of the topic, different approaches used to study the molecular mechanisms of hypoxia have many limitations. One promising lead is the use of various genetically encoded tools that allow for the observation of intracellular parameters in living systems. In the first part of this review, we provide the classification of oxygen/hypoxia reporters as well as describe other genetically encoded reporters for various metabolic and redox parameters that could be implemented in hypoxia studies. In the second part, we discuss the advantages and disadvantages of the primary hypoxia model systems and highlight inspiring examples of research in which these experimental settings were combined with genetically encoded reporters.

The Diverse Roles of Phagocytes During Bacterial and Fungal Infections and Sterile Inflammation: Lessons From Zebrafish

The immediate and natural reaction to both infectious challenges and sterile insults (wounds, tissue trauma or crystal deposition) is an acute inflammatory response. This inflammatory response is mediated by activation of the innate immune system largely comprising professional phagocytes (neutrophils and macrophages). Zebrafish (danio rerio) larvae possess many advantages as a model organism, including their genetic tractability and highly conserved innate immune system. Exploiting these attributes and the live imaging potential of optically transparent zebrafish larvae has greatly contributed to our understanding of how neutrophils and macrophages orchestrate the initiation and resolution phases of inflammatory responses. Numerous bacterial and fungal infection models have been successfully established using zebrafish as an animal model and studies investigating neutrophil and macrophage behavior to sterile insults have also provided unique insights. In this review we highlight how examining the larval zebrafish response to specific bacterial and fungal pathogens has uncovered cellular and molecular mechanisms behind a variety of phagocyte responses, from those that protect the host to those that are detrimental. We also describe how modeling sterile inflammation in larval zebrafish has provided an opportunity to dissect signaling pathways that control the recruitment, and fate, of phagocytes at inflammatory sites. Finally, we briefly discuss some current limitations, and opportunities to improve, the zebrafish model system for studying phagocyte biology.

DnaJ-PKAc fusion induces liver inflammation in a zebrafish model of fibrolamellar carcinoma

Fibrolamellar carcinoma (FLC) is a rare liver cancer that affects adolescents and young adults. Genomic analysis of FLC has revealed a 400 kb deletion in chromosome 19 that leads to the chimeric transcript DNAJB1-PRKACA (DnaJ-PKAc), comprised of the first exon of heat shock protein 40 (DNAJB1) and exons 2-10 of the catalytic subunit of protein kinase A (PRKACA). Here, we report a new zebrafish model of FLC induced by ectopic expression of zebrafish Dnaja-Pkaca (zfDnaJa-Pkaca) in hepatocytes that is amenable to live imaging of early innate immune inflammation. Expression of zfDnaJa-Pkaca in hepatocytes induces hepatomegaly and increased hepatocyte size. In addition, FLC larvae exhibit early innate immune inflammation characterized by early infiltration of neutrophils and macrophages into the liver microenvironment. Increased Caspase-a (the zebrafish homolog for human caspase-1) activity was also found in the liver of FLC larvae, and pharmacological inhibition of Tnfα and caspase-a decreased liver size and inflammation. Overall, these findings show that innate immune inflammation is an early feature in a zebrafish model of FLC and that pharmacological inhibition of TNFα or caspase-1 activity might be targets to treat inflammation and progression in FLC patients.This article has an associated First Person interview with the first author of the paper.

Hydrogen peroxide in neutrophil inflammation: Lesson from the zebrafish

The zebrafish has become an excellent model for the study of inflammation and immunity. Its unique advantages for in vivo imaging and gene and drug screening have allowed the visualization of dual oxidase 1 (Duox1)-derived hydrogen peroxide (H₂O₂) tissue gradients and its crosstalk with neutrophil infiltration to inflamed tissue. Thus, it has been shown that H₂O₂ directly recruits neutrophils via the Src-family tyrosine kinase Lyn and indirectly by the activation of several signaling pathways involved in inflammation, such as nuclear factor κB (NF-κB), mitogen activated kinases and the transcription factor AP1. In addition, this model has also unmasked the unexpected ability of H₂O₂ to induce the expression of the gene encoding the key neutrophil chemoattractant CXC chemokine ligand 8 by facilitating the accessibility of transcription factors to its promoter through histone covalent modifications. Finally, zebrafish models of psoriasis have shown that a H₂O₂/NF-κB/Duox1 positive feedback inflammatory loop operates in this chronic inflammatory disorder and that pharmacological inhibition of Duox1, but not of downstream mediators, inhibits inflammation and restores epithelial homeostasis. Therefore, these results have pointed out DUOX1 and H₂O₂ as therapeutic targets for the treatment of skin inflammatory disorders, such as psoriasis.

Redox regulation of tyrosine kinase signalling: more than meets the eye

Protein kinases are essential mediators of cellular signal transduction and are often dysregulated in disease. Among these, protein tyrosine kinases (PTKs) have received specific interest due to their common roles in various diseases including cancer, and emerging observations indicating that PTK signalling pathways are susceptible to regulation by reactive oxygen species (ROS), which are also frequently implicated in disease pathology. While it is well recognized that ROS can impact on tyrosine kinase signalling by inhibiting tyrosine phosphatases, more recent studies highlight additional modes of redox-based regulation of tyrosine kinase signalling by direct redox modification of non-catalytic cysteines within tyrosine kinases or other protein components of this signalling pathway. In this review, we will present recent advancements with respect to redox-based mechanisms in regulating PTK signalling, with a specific focus on recent studies demonstrating direct redox regulation of Src-family kinases and epidermal growth factor receptor kinases. Importantly, redox-based modulation of tyrosine kinases may be relevant for many other kinases and has implications for current approaches to develop pharmacological inhibitors for these proteins.

Three Ingredients of Safflower Alleviate Acute Lung Injury and Inhibit NET Release Induced by Lipopolysaccharide

Xuebijing injection is a Chinese herb compound to treat sepsis in China, but it contains many different kinds of components, and each component may have different effects in treating sepsis. The present study was performed to investigate the effect of three ingredients of Xuebijing, safflor yellow A (SYA), hydroxysafflor yellow A (HSYA), and anhydrosafflor yellow B (AHSYB), in lipopolysaccharide- (LPS-) induced acute lung injury (ALI). LPS (10 mg/kg) was injected intratracheally to induce acute lung injury in mice, which were then treated with SYA, HSYA, and AHSYB. The blood, bronchoalveolar lavage fluid (BALF), and lung tissues were collected to detect degree of lung injury, level of inflammation, and neutrophil extracellular traps (NETs). In vitro experiments were performed using HL-60 cells stimulated with phorbol myristate acetate (PMA). Lung injury induced by LPS was alleviated by SYA, HSYA, and AHSYB as demonstrated by the histopathologic test. The three components inhibit LPS-induced elevation of the levels of inflammatory factors and wet-to-dry weight ratio as well as the amount of protein and cells in the BALF. They also induced a remarkably less overlay of myeloperoxidase (MPO) and histone in the immunofluorescence assay and reduced level of MPO-DNA complex in plasma. The in vitro assay showed a similar trend that the three components inhibited PMA-induced NET release in neutrophil-like HL-60 cells. Western blot demonstrated that phosphorylation of c-rapidly accelerated fibrosarcoma (c-Raf), mitogen-activated protein kinase ERK kinase (MEK), and extracellular signal-regulated kinase (ERK) in the lungs of LPS-challenged mice, and PMA-treated HL-60 cells were all significantly reduced by SYA, HSYA, and AHSYB. Therefore, our data demonstrated that three components of XBJ, including SYA, HSYA, and AHSYB, showed a protective effect against LPS-induced lung injury and NET release.

The Effect of Fluence on Macrophage Kinetics, Oxidative Stress, and Wound Closure Using Real-Time In Vivo Imaging

Objective: The aim of our study was to quantify the effect of doses delivered by a He:Ne laser on individual macrophage kinetics, tissue oxidative stress, and wound closure using real-time in vivo imaging. Background: Photobiomodulation has been reported to reduce tissue inflammation and accelerate wound closure; however, precise parameters of laser settings to optimize macrophage behavior have not been established. We hypothesized that quantitative and real-time in vivo imaging could identify optimal fluence for macrophage migration, reduction of reactive oxygen species, and acceleration of wound closure. Methods: Larval zebrafish Tg(mpeg-dendra2) were loaded with dihydroethidium for oxidative stress detection. Fish were caudal fin injured, treated with 635 nm continuous 5 mW He:Ne laser irradiation at 3, 9, or 18 J/cm² and time-lapsed imaged within the first 120 min postinjury. Images taken 1 and 24-h postinjury were compared for percentage wound closure. Results: A fluence of 3 J/cm² demonstrated significant increases in macrophage migration speed, fewer stops along the way, and greatest directed migration toward the wound. These findings were associated with a significant reduction in wound content reactive oxygen species when compared with control wounded fins. Both 3 and 9 J/cm² significantly accelerated wound closure when compared with nonirradiated control fish. Conclusions: Wound macrophage activity could be manipulated by applied fluence, leading to reduced levels of wound reactive oxygen species and accelerated wound closure. The zebrafish model provides a means to quantitatively compare wound macrophage behavior in response to a variety of laser treatment parameters in real time.

The myeloid lineage is required for the emergence of a regeneration-permissive environment following Xenopus tail amputation

Regeneration-competent vertebrates are considered to suppress inflammation faster than non-regenerating ones. Hence, understanding the cellular mechanisms affected by immune cells and inflammation can help develop strategies to promote tissue repair and regeneration. Here, we took advantage of naturally occurring tail regeneration-competent and -incompetent developmental stages of Xenopus tadpoles. We first establish the essential role of the myeloid lineage for tail regeneration in the regeneration-competent tadpoles. We then reveal that upon tail amputation there is a myeloid lineage-dependent change in amputation-induced apoptosis levels, which in turn promotes tissue remodelling, and ultimately leads to the relocalization of the regeneration-organizing cells responsible for progenitor proliferation. These cellular mechanisms failed to be executed in regeneration-incompetent tadpoles. We demonstrate that regeneration incompetency is characterized by inflammatory myeloid cells whereas regeneration competency is associated with reparative myeloid cells. Moreover, treatment of regeneration-incompetent tadpoles with immune-suppressing drugs restores myeloid lineage-controlled cellular mechanisms. Collectively, our work reveals the effects of differential activation of the myeloid lineage on the creation of a regeneration-permissive environment and could be further exploited to devise strategies for regenerative medicine purposes.

Summary:Xenopus tail regeneration requires a hierarchy of cellular events initiated by the myeloid lineage and culminating in the mobilization of regeneration-organizing cells.

Signaling Response to Transient Redox Stress in Human Isolated T Cells: Molecular Sensor Role of Syk Kinase and Functional Involvement of IL2 Receptor and L-Selectine

Reactive oxygen species (ROS) are central effectors of inflammation and play a key role in cell signaling. Previous reports have described an association between oxidative events and the modulation of innate immunity. However, the role of redox signaling in adaptive immunity is still not well understood. This work is based on a novel investigation of diamide, a specific oxidant of sulfhydryl groups, and it is the first performed in purified T cell tyrosine phosphorylation signaling. Our data show that ex vivo T cells respond to –SH group oxidation with a distinctive tyrosine phosphorylation response and that these events elicit specific cellular responses. The expression of two essential T-cell receptors, CD25 and CD62L, and T-cell cytokine release is also affected in a specific way. Experiments with Syk inhibitors indicate a major contribution of this kinase in these phenomena. This pilot work confirms the presence of crosstalk between oxidation of cysteine residues and tyrosine phosphorylation changes, resulting in a series of functional events in freshly isolated T cells. Our experiments show a novel role of Syk inhibitors in applying their anti-inflammatory action through the inhibition of a ROS-generated reaction.

Phagocytosis of Necrotic Debris at Sites of Injury and Inflammation

Clearance of cellular debris is required to maintain the homeostasis of multicellular organisms. It is intrinsic to processes such as tissue growth and remodeling, regeneration and resolution of injury and inflammation. Most of the removal of effete and damaged cells is performed by macrophages and neutrophils through phagocytosis, a complex phenomenon involving ingestion and degradation of the disposable particles. The study of the clearance of cellular debris has been strongly biased toward the removal of apoptotic bodies; as a result, the mechanisms underlying the removal of necrotic cells have remained relatively unexplored. Here, we will review the incipient but growing knowledge of the phagocytosis of necrotic debris, from their recognition and engagement to their internalization and disposal. Critical insights into these events were gained recently through the development of new in vitro and in vivo models, along with advances in live-cell and intravital microscopy. This review addresses the classes of "find-me" and "eat-me" signals presented by necrotic cells and their cognate receptors in phagocytes, which in most cases differ from the extensively characterized counterparts in apoptotic cell engulfment. The roles of damage-associated molecular patterns, chemokines, lipid mediators, and complement components in recruiting and activating phagocytes are reviewed. Lastly, the physiological importance of necrotic cell removal is emphasized, highlighting the key role of impaired debris clearance in autoimmunity.

Glutathione peroxidase-1 regulates adhesion and metastasis of triple-negative breast cancer cells via FAK signaling

Triple-negative breast cancer (TNBC) cells, which do not express genes for estrogen receptor (ER), progesterone receptor (PR), and Her2/neu, develop highly aggressive and metastatic tumors resistant to chemo- and hormonal therapies. We found that expression of glutathione peroxidase-1 (Gpx1) is silenced in the non-TNBC cells but significantly maintained in the TNBC cell lines. Such Gpx1 expression plays a vital role in the metastasis of TNBC cells by regulating cell adhesion. Transcriptomic and signaling pathway analyses demonstrate that depletion of Gpx1 essentially impairs cell adhesion/spreading by down-regulating FAK/c-Src activation. Mechanistically, Gpx1 interacts with FAK kinase and prevents the kinase inactivation by H₂O₂, not lipid hydroperoxide. As a result, depletion of Gpx1 suppresses lung metastasis of TNBC cells in vivo. Overall, our study identifies that Gpx1 is a redox safeguard of FAK kinase and its inhibition may provide an effective way to control the metastasis of deadly malignant TNBC.

Acid Sphingomyelinase regulates the localization and trafficking of palmitoylated proteins

In human, loss of acid sphingomyelinase (ASM/SMPD1) causes Niemann–Pick disease, type A. ASM hydrolyzes sphingomyelins to produce ceramides but protein targets of ASM remain largely unclear. Our mass spectrometry-based proteomic analyses have identified >100 proteins associated with the ASM-dependent, detergent-resistant membrane microdomains (lipid rafts), with >60% of these proteins being palmitoylated, including SNAP23, Src-family kinases Yes and Lyn, and Ras and Rab family small GTPases. Inactivation of ASM abolished the presence of these proteins in the plasma membrane, with many of them trapped in the Golgi. While palmitoylation inhibitors and palmitoylation mutants phenocopied the effects of ASM inactivation, we demonstrated that ASM is required for the transport of palmitoylated proteins, such as SNAP23 and Lyn, from the Golgi to the plasma membrane without affecting palmitoylation directly. Importantly, ASM delivered extracellularly can regulate the trafficking of SNAP23 from the Golgi to the plasma membrane. Our studies suggest that ASM, acting at the plasma membrane to produce ceramides, regulates the localization and trafficking of the palmitoylated proteins.

Summary: Acid sphingomyelinase (ASM) regulates palmitoylated protein trafficking and localization.

Physical plasma and leukocytes - immune or reactive?

Leukocytes are professionals in recognizing and removing pathogenic or unwanted material. They are present in virtually all tissues, and highly motile to enter or leave specific sites throughout the body. Less than a decade ago, physical plasmas entered the field of medicine to deliver their delicate mix of reactive species and other physical agents for mainly dermatological or oncological therapy. Plasma treatment thus affects leukocytes via direct or indirect means: immune cells are either present in tissues during treatment, or infiltrate or exfiltrate plasma-treated areas. The immune system is crucial for human health and resolution of many types of diseases. It is therefore vital to study the response of leukocytes after plasma treatment in vitro and in vivo. This review gathers together the major themes in the plasma treatment of innate and adaptive immune cells, and puts these into the context of wound healing and oncology, the two major topics in plasma medicine.

Proteogenomic landscape of squamous cell lung cancer

How genomic and transcriptomic alterations affect the functional proteome in lung cancer is not fully understood. Here, we integrate DNA copy number, somatic mutations, RNA-sequencing, and expression proteomics in a cohort of 108 squamous cell lung cancer (SCC) patients. We identify three proteomic subtypes, two of which (Inflamed, Redox) comprise 87% of tumors. The Inflamed subtype is enriched with neutrophils, B-cells, and monocytes and expresses more PD-1. Redox tumours are enriched for oxidation-reduction and glutathione pathways and harbor more NFE2L2/KEAP1 alterations and copy gain in the 3q2 locus. Proteomic subtypes are not associated with patient survival. However, B-cell-rich tertiary lymph node structures, more common in Inflamed, are associated with better survival. We identify metabolic vulnerabilities (TP63, PSAT1, and TFRC) in Redox. Our work provides a powerful resource for lung SCC biology and suggests therapeutic opportunities based on redox metabolism and immune cell infiltrates.

Squamous cell lung cancer has dismal prognosis due to the dearth of effective treatments. Here, the authors perform an integrated proteogenomic analysis of the disease, revealing three proteomics-based subtypes and suggesting potential therapeutic opportunities.

Models of human psoriasis: Zebrafish the newly appointed player

Psoriasis is a human chronic, immune disease with severe cutaneous and systemic manifestations. Its prevalence, among the world population, highly varies with ethnicity and geography, but not sex from remarkable low levels in Asia to 2.3% in Spain, or an impressive 11.5% in Norway. The pathogenesis of psoriasis derives from complex genetic and environmental interactions, which creates aberrant crosstalk between keratinocytes and variated immune cell, resulting in open amplified inflammatory and pro-proliferative circuits. Both, innate and adaptive immune systems are known to be involved in the response at the cellular and humoral levels. Nevertheless, the exact molecular mechanisms are still under debate. Therefore, discovering useful therapeutic targets to stretch the molecular gaps in psoriasis pathogenesis and its associated comorbidities is still mandatory. So far, some mutagenic or pharmacological studies in vitro or using comparative vertebrate models have provided critical molecular insights and directed the human research. Although highly feasible in rodents, the versatile physiology, genetic similarity to humans and outstanding molecular toolbox available, suggest that elaborate forward genetic screenings are far easier to be conducted using the zebrafish model. Thus, in this review, we intend to briefly overview psoriasis and revise in a digested fashion the preclinical research models available, emphasizing the zebrafish as a powerful tool in the study of immune effectors on the same, and how it supports the discovering of new therapies that may help in controlling this widespread disease around the globe.

Loss of Function of DOCK4 in Myelodysplastic Syndromes Stem Cells is Restored by Inhibitors of DOCK4 Signaling Networks

PURPOSE

Myelodysplastic syndromes (MDS) with deletion of chromosome 7q/7 [-7/(del)7q MDS] is associated with worse outcomes and needs novel insights into pathogenesis. Reduced expression of signaling protein dedicator of cytokinesis 4 (DOCK4) in patients with -7/(del)7q MDS leads to a block in hematopoietic stem cell (HSC) differentiation. Identification of targetable signaling networks downstream of DOCK4 will provide means to restore hematopoietic differentiation in MDS.Experimental Design: We utilized phosphoproteomics approaches to identify signaling proteins perturbed as a result of reduced expression of DOCK4 in human HSCs and tested their functional significance in primary model systems.

RESULTS

We demonstrate that reduced levels of DOCK4 lead to increased global tyrosine phosphorylation of proteins in primary human HSCs. LYN kinase and phosphatases INPP5D (SHIP1) and PTPN6 (SHP1) displayed greatest levels of tyrosine phosphorylation when DOCK4 expression levels were reduced using DOCK4-specific siRNA. Our data also found that increased phosphorylation of SHIP1 and SHP1 phosphatases were due to LYN kinase targeting these phosphatases as substrates. Increased migration and impediment of HSC differentiation were consequences of these signaling alterations. Pharmacologic inhibition of SHP1 reversed these functional aberrations in HSCs expressing low DOCK4 levels. In addition, differentiation block seen in DOCK4 haplo-insufficient [-7/(del)7q] MDS was rescued by inhibition of SHP1 phosphatase.

CONCLUSIONS

LYN kinase and phosphatases SHP1 and SHIP1 are perturbed when DOCK4 expression levels are low. Inhibition of SHP1 promotes erythroid differentiation in healthy HSCs and in -7/(del)7q MDS samples with low DOCK4 expression. Inhibitors of LYN, SHP1 and SHIP1 also abrogated increased migratory properties in HSCs expressing reduced levels of DOCK4.

Distinct inflammatory and wound healing responses to complex caudal fin injuries of larval zebrafish

Wound repair is controlled temporally and spatially to restore tissue homeostasis. Previously we reported that thermal damage of the larval zebrafish fin disrupts collagen organization and wound healing compared to tail transection (LeBert et al., 2018). Here we characterize different injury models in larval zebrafish to dissect temporal and spatial dynamics of repair in complex damage. We found that each damage model triggers distinct inflammatory and tissue responses, with Stat3 and TGFβ playing key roles in the regulation of mesenchymal cells during simple repair. While thermal injury disrupts collagen fibers initially, healing is recovered as inflammation resolves, and mesenchymal cells and collagen fibers align. By contrast, infected wounds lead to persistent inflammation and loss of mesenchymal cells, resulting in minimal tissue repair. These wound models have broad physiological relevance, thereby providing a valuable advance in our toolkit to probe the dynamics of inflammation and wound repair in complex tissue damage.

Dual roles of hydrogen peroxide in promoting zebrafish renal repair and regeneration

Acute renal injury (AKI) is a serious disorder of renal failure or renal damage that occurs within hours or days. At present, there is no approved pharmaceutical treatment for AKI. Zebrafish is an excellent model for studying the repair of AKI because of its remarkable ability to repair kidney injury. Using zebrafish AKI model inducing by gentamicin, we found that hydrogen peroxide (H₂O₂) plays dual roles during the period of AKI recovery including renal repair and kidney regeneration. In the repair stage of AKI, H₂O₂ was produced in proximal and distal segments of renal tubules. By inhibiting H₂O₂ generation using Duox Vivo-Morpholino or chemical inhibitor, it was observed of severe damage of renal tubules, and extensive cell apoptosis. In the stage of regeneration, we found that H₂O₂ was highly generated in renal interstitium. Inhibiting production of H₂O₂ could significantly down-regulate the ability of kidney regeneration, which was associated with the failure of proliferation of renal progenitor cells. Therefore, H₂O₂ acts as a protective factor in renal repair and an initial signal of kidney regeneration, indicating the key roles of H₂O₂ in promoting recovery of AKI in zebrafish.

Quantitative Imaging of Endogenous and Exogenous H2O2 Gradients in Live Zebrafish Larvae

Quantitative aspects of extracellular H₂O₂ signaling in animals, such as its spatiotemporal dynamics within tissues, remain little understood. Here we detail an optimized, experimental setup for measuring the dynamics and physiological consequences of extracellular H₂O₂ application to live tissues by intravital biosensor imaging in zebrafish larvae.

Cytoskeletal Exposure in the Regulation of Immunity and Initiation of Tissue Repair

This article reviews and discusses emerging evidence suggesting an evolutionarily-conserved connection between injury-associated exposure of cytoskeletal proteins and the induction of tolerance to infection, repair of tissue damage and restoration of homeostasis. While differences exist between vertebrates and invertebrates with respect to the receptor(s), cell types, and effector mechanisms involved, the response to exposed cytoskeletal proteins appears to be protective and to rely on a conserved signaling cassette involving Src family kinases, the nonreceptor tyrosine kinase Syk, and tyrosine phosphatases. A case is made for research programs that integrate different model organisms in order to increase the understanding of this putative response to tissue damage.

Glucocorticoids inhibit macrophage differentiation towards a pro-inflammatory phenotype upon wounding without affecting their migration

Glucocorticoid drugs are widely used to treat immune-related diseases, but their use is limited by side effects and by resistance, which especially occurs in macrophage-dominated diseases. In order to improve glucocorticoid therapies, more research is required into the mechanisms of glucocorticoid action. In the present study, we have used a zebrafish model for inflammation to study glucocorticoid effects on the innate immune response. In zebrafish larvae, the migration of neutrophils towards a site of injury is inhibited upon glucocorticoid treatment, whereas migration of macrophages is glucocorticoid resistant. We show that wounding-induced increases in the expression of genes that encode neutrophil-specific chemoattractants (Il8 and Cxcl18b) are attenuated by the synthetic glucocorticoid beclomethasone, but that beclomethasone does not attenuate the induction of the genes encoding Ccl2 and Cxcl11aa, which are required for macrophage recruitment. RNA sequencing on FACS-sorted macrophages shows that the vast majority of the wounding-induced transcriptional changes in these cells are inhibited by beclomethasone, whereas only a small subset is glucocorticoid-insensitive. As a result, beclomethasone decreases the number of macrophages that differentiate towards a pro-inflammatory (M1) phenotype, which we demonstrated using a tnfa:eGFP-F reporter line and analysis of macrophage morphology. We conclude that differentiation and migration of macrophages are regulated independently, and that glucocorticoids leave the chemotactic migration of macrophages unaffected, but exert their anti-inflammatory effect on these cells by inhibiting their differentiation to an M1 phenotype. The resistance of macrophage-dominated diseases to glucocorticoid therapy can therefore not be attributed to an intrinsic insensitivity of macrophages to glucocorticoids.

Summary: In a zebrafish model for inflammation, glucocorticoids do not affect the migration of macrophages, but inhibit their differentiation towards an M1 phenotype, by strongly attenuating transcriptional responses in these cells.

Understanding the Metabolic Profile of Macrophages During the Regenerative Process in Zebrafish

In contrast to mammals, lower vertebrates, including zebrafish (Danio rerio), have the ability to regenerate damaged or lost tissues, such as the caudal fin, which makes them an ideal model for tissue and organ regeneration studies. Since several diseases involve the process of transition between fibrosis and tissue regeneration, it is necessary to attain a better understanding of these processes. It is known that the cells of the immune system, especially macrophages, play essential roles in regeneration by participating in the removal of cellular debris, release of pro- and anti-inflammatory factors, remodeling of components of the extracellular matrix and alteration of oxidative patterns during proliferation and angiogenesis. Immune cells undergo phenotypical and functional alterations throughout the healing process due to growth factors and cytokines that are produced in the tissue microenvironment. However, some aspects of the molecular mechanisms through which macrophages orchestrate the formation and regeneration of the blastema remain unclear. In the present review, we outline how macrophages orchestrate the regenerative process in zebrafish and give special attention to the redox balance in the context of tail regeneration.

A highly specific and sensitive turn-on fluorescence probe for hypochlorite detection and its bioimaging applications

Development of high performance fluorescent chemosensors for the detection of ClO- in vitro and in vivo is very desirable, because many human diseases are caused by ClO-. In this paper, a highly selectivity and sensitive fluorescent probe, EDPC, based on 3-acetylcoumarin, was synthesized, which could respond to ClO- and exhibit an "off-on" mode in Tris-HCl buffer (pH = 7.2, 10 mM, 50% C2H5OH) solutions. The detection limit of the EDPC probe for ClO- was as low as 1.2 × 10-8 M. Moreover, the high selectivity and high sensitivity of EDPC towards ClO- are attributed to the oxidation reaction between the C-O of the coumarin lactone and the C[double bond, length as m-dash]C formed by aldol condensation and the mechanism was further verified using ESI-MS and DFT. Additionally, the concentrations of ClO- in real water were also calculated using the EDPC probe and showed good recovery. Finally, the distribution of intracellular endogenous ClO- was gained by confocal fluorescence microscopy in living HEK293T cells.

Simu-dependent clearance of dying cells regulates macrophage function and inflammation resolution

Macrophages encounter and clear apoptotic cells during normal development and homeostasis, including at numerous sites of pathology. Clearance of apoptotic cells has been intensively studied, but the effects of macrophage-apoptotic cell interactions on macrophage behaviour are poorly understood. Using Drosophila embryos, we have exploited the ease of manipulating cell death and apoptotic cell clearance in this model to identify that the loss of the apoptotic cell clearance receptor Six-microns-under (Simu) leads to perturbation of macrophage migration and inflammatory responses via pathological levels of apoptotic cells. Removal of apoptosis ameliorates these phenotypes, while acute induction of apoptosis phenocopies these defects and reveals that phagocytosis of apoptotic cells is not necessary for their anti-inflammatory action. Furthermore, Simu is necessary for clearance of necrotic debris and retention of macrophages at wounds. Thus, Simu is a general detector of damaged self and represents a novel molecular player regulating macrophages during resolution of inflammation.

Structure and mechanisms of ROS generation by NADPH oxidases

NADPH oxidases (NOXs) are integral membrane enzymes that produce reactive oxygen species. Humans have seven NOX enzymes that feature a very similar catalytic core but distinct regulatory mechanisms. The recent structural elucidation of the NOX catalytic domains has been a step forward in the field. NADPH, FAD, and two hemes form a linear array of redox cofactors that transfer electrons across to the two sides of the membrane. Oxygen is reduced through an unusual outer sphere mechanism that does not involve any covalent intermediate with the heme iron. Several recent studies have expanded the roles of NOXs in cell signaling, innate immune response, and cell proliferation including oncogenic transformation. This work reinforces NOX-generated ROS as powerful signaling molecules. A challenging question is to understand the specific mechanisms of enzyme regulation and to harness the growing insight on NOXs' structure and biochemistry to generate more powerful small-molecule modulators of NOX activities.

Zebrafish fin-derived fibroblast cell line: A model for in vitro wound healing

The goal of this study was to develop and characterize a cell line from the caudal fin tissue of zebrafish and also its application as an in vitro model to study the effect of H₂ O₂ in wound healing. Fibroblastic cell line was developed using explant culture method from caudal fin tissue of zebrafish and characterized. This cell line was named as DrF cell line. The DrF cells treated with 0-10 µM/ml H₂ O₂ were tested for viability, proliferation and motility by MTT assay, trypan blue assay and chemotaxis assay, respectively. Among the different concentrations of H₂ O₂ , 4 µM was found to be nontoxic to study cell migration in in vitro scratch wound assay. Furthermore, the expression of proliferating cell nuclear antigen (PCNA) and chemokine receptor (CXCR4) genes was carried by qPCR. The cell survival, proliferation and migration were extremely enriched at 4 µM level of H₂ O₂ . We observed accelerated wound closure in DrF cells treated with H₂ O_2. The qPCR results indicated that H₂ O₂ markedly up-regulated mRNA expression of PCNA and CXCR4. The findings from our study suggest that H₂ O₂ at low levels promotes cell survival, proliferation, migration and wound healing in DrF cells.

Two coumarin-based turn-on fluorescent probes based on for hypochlorous acid detection and imaging in living cells

This work, two turn-on fluorescent probes (3-acetyl-2H-chromen-2-one (ACO) & (1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (CETC)) based on coumarin have been designed and synthesized, which could selectively and sensitively recognize ClO^- with fast response time. ACO &CETC were almost non fluorescent possibly due to both the lacton form of coumarin and unbridged CN bonds which can undergo a nonradiative decay process in the excited state. Upon the addition of ClO^-, ACO &CETC were oxidized to ring - opened by cleavage the CO and CN and the fluorescence intensity were increased considerably. Fluorescence titration experiments showed that the detection limit ACO &CETC is as low as 22 nm and 51 nm respectively. In particular, some relevant reactive species, including OH, ¹O₂, H₂O₂, KO₂, some anions and cations cannot be interference with the test. In live cell experiments, ACO &CETC were successfully applied to image exogenous ClO^- in HepG2 cells. Therefore, ACO &CETC not only could image ClO^- in living cells but also proved that CO and CN can be cleavage by ClO^-.

Ena orchestrates remodelling within the actin cytoskeleton to drive robust Drosophila macrophage chemotaxis

The actin cytoskeleton is the engine that powers the inflammatory chemotaxis of immune cells to sites of tissue damage or infection. Here, we combine genetics with live in vivo imaging to investigate how cytoskeletal rearrangements drive macrophage recruitment to wounds in Drosophila. We find that the actin-regulatory protein Ena is a master regulator of lamellipodial dynamics in migrating macrophages, where it remodels the cytoskeleton to form linear filaments that can then be bundled together by the cross-linker Fascin (also known as Singed in flies). In contrast, the formin Dia generates rare, probing filopods for specialised functions that are not required for migration. The role of Ena in lamellipodial bundling is so fundamental that its overexpression increases bundling even in the absence of Fascin by marshalling the remaining cross-linking proteins to compensate. This reorganisation of the lamellipod generates cytoskeletal struts that push against the membrane to drive leading edge advancement and boost cell speed. Thus, Ena-mediated remodelling extracts the most from the cytoskeleton to power robust macrophage chemotaxis during their inflammatory recruitment to wounds.

Summary: Macrophages must migrate to a variety of stimuli, including inflammatory wounds. We identify the actin-regulatory protein Ena as a master remodeller of the cytoskeleton within migrating macrophages in vivo.

Drosophila as a Genetic Model for Hematopoiesis

In this FlyBook chapter, we present a survey of the current literature on the development of the hematopoietic system in Drosophila The Drosophila blood system consists entirely of cells that function in innate immunity, tissue integrity, wound healing, and various forms of stress response, and are therefore functionally similar to myeloid cells in mammals. The primary cell types are specialized for phagocytic, melanization, and encapsulation functions. As in mammalian systems, multiple sites of hematopoiesis are evident in Drosophila and the mechanisms involved in this process employ many of the same molecular strategies that exemplify blood development in humans. Drosophila blood progenitors respond to internal and external stress by coopting developmental pathways that involve both local and systemic signals. An important goal of these Drosophila studies is to develop the tools and mechanisms critical to further our understanding of human hematopoiesis during homeostasis and dysfunction.

Ask1 and Akt act synergistically to promote ROS-dependent regeneration in Drosophila

How cells communicate to initiate a regenerative response after damage has captivated scientists during the last few decades. It is known that one of the main signals emanating from injured cells is the Reactive Oxygen Species (ROS), which propagate to the surrounding tissue to trigger the replacement of the missing cells. However, the link between ROS production and the activation of regenerative signaling pathways is not yet fully understood. We describe here the non-autonomous ROS sensing mechanism by which living cells launch their regenerative program. To this aim, we used Drosophila imaginal discs as a model system due to its well-characterized regenerative ability after injury or cell death. We genetically-induced cell death and found that the Apoptosis signal-regulating kinase 1 (Ask1) is essential for regenerative growth. Ask1 senses ROS both in dying and living cells, but its activation is selectively attenuated in living cells by Akt1, the core kinase component of the insulin/insulin-like growth factor pathway. Akt1 phosphorylates Ask1 in a secondary site outside the kinase domain, which attenuates its activity. This modulation of Ask1 activity results in moderate levels of JNK signaling in the living tissue, as well as in activation of p38 signaling, both pathways required to turn on the regenerative response. Our findings demonstrate a non-autonomous activation of a ROS sensing mechanism by Ask1 and Akt1 to replace the missing tissue after damage. Collectively, these results provide the basis for understanding the molecular mechanism of communication between dying and living cells that triggers regeneration.

One of the early events that occur after tissue damage consists on the production of Reactive Oxygen Species (ROS), that signal to the surrounding tissue to initiate wound healing and regeneration. Many signaling pathways, such as JNK and p38, respond to oxidative stress and are necessary for regenerative growth. As the link between ROS and regenerative signaling is not well understood, we decided to explore the mechanism that underlies this process. To do that, we genetically induced cell death in specific areas of Drosophila wing imaginal discs and then studied the mechanism that drives living cells to replace the damage zone until it is completely regenerated. We found that the Drosophila Apoptosis signal-regulating kinase 1 (Ask1), a protein that is sensitive to oxidative stress, is a key player in this scenario. This protein acts as an intracellular sensor that upon damage activates the JNK and p38 regenerative signaling pathways. However, high activity of Ask1 can be toxic for the cell. This is controlled by Akt, a kinase downstream the insulin pathway, which attenuates the activity of Ask1 in the living cells that will participate in the regeneration process. In consequence, Ask1 and Akt act synergistically to respond to the stress generated after tissue damage and drive regeneration. Our results provide a first overview within the framework of how insulin signaling inputs could modulate the capacity to overcome tissue damage.

From aggregation-induced to solution emission: a new strategy for designing ratiometric fluorescent probes and its application for in vivo HClO detection

The fluorescence of aggregation-induced emission is converted into that from ICT-induced emission in the presence of HClO.

NADPH-Oxidase-derived reactive oxygen species are required for cytoskeletal organization, proper localization of E-cadherin and cell motility during zebrafish epiboly

Cell movements are essential for morphogenesis during animal development. Epiboly is the first morphogenetic process in zebrafish in which cells move en masse to thin and spread the deep and enveloping cell layers of the blastoderm over the yolk cell. While epiboly has been shown to be controlled by complex molecular networks, the contribution of reactive oxygen species (ROS) to this process has not previously been studied. Here, we show that ROS are required for epiboly in zebrafish. Visualization of ROS in whole embryos revealed dynamic patterns during epiboly progression. Significantly, inhibition of NADPH oxidase activity leads to a decrease in ROS formation, delays epiboly, alters E-cadherin and cytoskeleton patterns and, by 24 h post-fertilization, decreases embryo survival, effects that are rescued by hydrogen peroxide treatment. Our findings suggest that a delicate ROS balance is required during early development and that disruption of that balance interferes with cell adhesion, leading to defective cell motility and epiboly progression.

Phenylboronic acid derivative-modified (6,5) single-wall carbon nanotube probes for detecting glucose and hydrogen peroxide

In this paper, we presented a new method for constructing near-infrared fluorescence probes and their applications in detecting glucose and hydrogen peroxide (H₂O₂).

Hydrogen Peroxide and Redox Regulation of Developments

Reactive oxygen species (ROS), which were originally classified as exclusively deleterious compounds, have gained increasing interest in the recent years given their action as bona fide signalling molecules. The main target of ROS action is the reversible oxidation of cysteines, leading to the formation of disulfide bonds, which modulate protein conformation and activity. ROS, endowed with signalling properties, are mainly produced by NADPH oxidases (NOXs) at the plasma membrane, but their action also involves a complex machinery of multiple redox-sensitive protein families that differ in their subcellular localization and their activity. Given that the levels and distribution of ROS are highly dynamic, in part due to their limited stability, the development of various fluorescent ROS sensors, some of which are quantitative (ratiometric), represents a clear breakthrough in the field and have been adapted to both ex vivo and in vivo applications. The physiological implication of ROS signalling will be presented mainly in the frame of morphogenetic processes, embryogenesis, regeneration, and stem cell differentiation. Gain and loss of function, as well as pharmacological strategies, have demonstrated the wide but specific requirement of ROS signalling at multiple stages of these processes and its intricate relationship with other well-known signalling pathways.

A light-gated potassium channel for sustained neuronal inhibition

Currently available inhibitory optogenetic tools provide short and transient silencing of neurons, but they cannot provide long-lasting inhibition because of the requirement for high light intensities. Here we present an optimized blue-light-sensitive synthetic potassium channel, BLINK2, which showed good expression in neurons in three species. The channel is activated by illumination with low doses of blue light, and in our experiments it remained active over (tens of) minutes in the dark after the illumination was stopped. This activation caused long periods of inhibition of neuronal firing in ex vivo recordings of mouse neurons and impaired motor neuron response in zebrafish in vivo. As a proof-of-concept application, we demonstrated that in a freely moving rat model of neuropathic pain, the activation of a small number of BLINK2 channels caused a long-lasting (>30 min) reduction in pain sensation.

Cellular mechanisms and signals that coordinate plasma membrane repair

Plasma membrane forms the barrier between the cytoplasm and the environment. Cells constantly and selectively transport molecules across their plasma membrane without disrupting it. Any disruption in the plasma membrane compromises its selective permeability and is lethal, if not rapidly repaired. There is a growing understanding of the organelles, proteins, lipids, and small molecules that help cells signal and efficiently coordinate plasma membrane repair. This review aims to summarize how these subcellular responses are coordinated and how cellular signals generated due to plasma membrane injury interact with each other to spatially and temporally coordinate repair. With the involvement of calcium and redox signaling in single cell and tissue repair, we will discuss how these and other related signals extend from single cell repair to tissue level repair. These signals link repair processes that are activated immediately after plasma membrane injury with longer term processes regulating repair and regeneration of the damaged tissue. We propose that investigating cell and tissue repair as part of a continuum of wound repair mechanisms would be of value in treating degenerative diseases.

Damage-induced reactive oxygen species enable zebrafish tail regeneration by repositioning of Hedgehog expressing cells

Many aquatic vertebrates have a remarkable ability to regenerate limbs and tails after amputation. Previous studies indicate that reactive oxygen species (ROS) signalling initiates regeneration, but the mechanism by which this takes place is poorly understood. Developmental signalling pathways have been shown to have proregenerative roles in many systems. However, whether these are playing roles that are specific to regeneration, or are simply recapitulating their developmental functions is unclear. Here, we analyse zebrafish larval tail regeneration and find evidence that ROS released upon wounding cause repositioning of notochord cells to the damage site. These cells secrete Hedgehog ligands that are required for regeneration. Hedgehog signalling is not required for normal tail development suggesting that it has a regeneration-specific role. Our results provide a model for how ROS initiate tail regeneration, and indicate that developmental signalling pathways can play regenerative functions that are not directly related to their developmental roles.

Reactive oxygen species (ROS) are required to initiate regeneration but the mechanisms regulating its production are unclear. Here, the authors show in zebrafish larval tail regeneration that ROS is released by mobilised notochord cells enables their repositioning in the damage site, assisted by secreted Hh.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Oxidant Signaling Mediated by Nox2 in Neutrophils Promotes Regenerative Myelopoiesis and Tissue Recovery following Ischemic Damage

Ischemic tissue damage activates hematopoietic stem and progenitor cells (HSPCs) in the bone marrow (BM)-generating myeloid cells, and persistent HSPC activity may drive chronic inflammation and impair tissue recovery. Although increased reactive oxygen species in the BM regulate HSPC functions, their roles in myelopoiesis of activated HSPCs and subsequent tissue recovery during ischemic damage are not well understood. In this paper, we report that deletion of Nox2 NADPH oxidase in mice results in persistent elevations in BM HSPC activity and levels of inflammatory monocytes/macrophages in BM and ischemic tissue in a model of hindlimb ischemia. Ischemic tissue damage induces oxidants in BM such as elevations of hydrogen peroxide and oxidized phospholipids, which activate redox-sensitive Lyn kinase in a Nox2-dependent manner. Moreover, during tissue recovery after ischemic injury, this Nox2-ROS-Lyn kinase axis is induced by Nox2 in neutrophils that home to the BM, which inhibits HSPC activity and inflammatory monocyte generation and promotes tissue regeneration after ischemic damage. Thus, oxidant signaling in the BM mediated by Nox2 in neutrophils regulates myelopoiesis of HSPCs to promote regeneration of damaged tissue.

Inflammation-on-a-Chip: Probing the Immune System Ex Vivo

Inflammation is the typical result of activating the host immune system against pathogens, and it helps to clear microbes from tissues. However, inflammation can occur in the absence of pathogens, contributing to tissue damage and leading to disease. Understanding how immune cells coordinate their activities to initiate, modulate, and terminate inflammation is key to developing effective interventions to preserve health and combat diseases. Towards this goal, inflammation-on-a-chip tools provide unique features that greatly benefit the study of inflammation. They reconstitute tissue environments in microfabricated devices and enable real-time, high-resolution observations and quantification of cellular activities relevant to inflammation. We review here recent advances in inflammation-on-a-chip technologies and highlight the biological insights and clinical applications enabled by these emerging tools.

In Vivo Imaging of Hydrogen Peroxide with HyPer Probes

SIGNIFICANCE

Hydrogen peroxide (H₂O₂) is a key signaling molecule involved in the regulation of both physiological and pathological cellular processes. Genetically encoded HyPer probes are currently among the most effective approaches for monitoring H₂O₂ dynamics in various biological systems because they can be easily targeted to specific cells and organelles. Since its development in 2006, HyPer has proved to be a robust and powerful tool in redox biology research. Recent Advances: HyPer probes were used in a variety of models to study the role of H₂O₂ in various redox processes. HyPer has been increasingly used in the past few years for in vivo studies, which has already led to many important discoveries, for example, that H₂O₂ plays a key role in the regulation of signaling cascades involved in development and aging, inflammation, regeneration, photosynthetic signaling, and other biological processes.

CRITICAL ISSUES

In this review, we focus on the main achievements in the field of redox biology that have been obtained from in vivo experiments using HyPer probes.

FUTURE DIRECTIONS

Further in vivo studies of the role of H₂O₂ largely depend on the development of more suitable versions of HyPer for in vivo models: those having brighter fluorescence and a more stable signal in response to physiological changes in pH. Antioxid. Redox Signal. 29, 569-584.

An unexpected friend - ROS in apoptosis-induced compensatory proliferation: Implications for regeneration and cancer

Apoptosis-induced compensatory proliferation (AiP) is a form of compensatory proliferation that is triggered by apoptotic cell death to maintain tissue homeostasis. As such, AiP is essential for many tissue repair processes including regeneration. The apoptotic effectors, termed caspases, not only execute apoptosis, but are also directly involved in the generation of the signals required for AiP. Reactive oxygen species (ROS) play an important role for regenerative processes. Recently, it was shown in Drosophila that apoptotic caspases can mediate the generation of ROS for promoting AiP. This review summarizes and discusses these findings in the context of regenerative processes and cancer.