Live imaging of innate immune cell sensing of transformed cells in zebrafish larvae: parallels between tumor initiation and wound inflammation

Retinal microglia signaling affects Müller cell behavior in the zebrafish following laser injury induction

Microglia are the resident tissue macrophages of the central nervous system including the retina. Under pathophysiological conditions, microglia can signal to Müller cells, the major glial component of the retina, affecting their morphological, molecular, and functional responses. Microglia-Müller cell interactions appear to be bidirectional shaping the overall injury response in the retina. Hence, microglia and Müller cell responses to disease and injury have been ascribed both positive and negative outcomes. However, Müller cell reactivity and survival in the absence of immune cells after injury have not been investigated in detail in adult zebrafish. Here, we develop a model of focal retinal injury combined with pharmacological treatments for immune cell depletion in zebrafish. The retinal injury was induced by a diode laser to damage photoreceptors. Two pharmacological treatments were used to deplete either macrophage-microglia (PLX3397) or selectively eliminate peripheral macrophages (clodronate liposomes). We show that PLX3397 treatment hinders retinal regeneration in zebrafish, which is reversed by microglial repopulation. On the other hand, selective macrophage elimination did not affect the kinetics of retinal regeneration. The absence of retinal microglia and macrophages leads to dysregulated Müller cell behavior. In the untreated fish, Müller cells react after injury induction showing glial fibrillary acidic protein (GFAP), Phospho-p44/42 MAPK (Erk1/2), and PCNA upregulation. However, in the immunosuppressed animals, GFAP and phospho-p44/42 MAPK (Erk1/2) expression was not upregulated overtime and the reentry in the cell cycle was not affected. Thus, microglia and Müller cell signaling is pivotal to unlock the regenerative potential of Müller cells in order to repair the damaged retina.

Imaging the neutrophil: Intravital microscopy provides a dynamic view of neutrophil functions in host immunity

Neutrophils are the first cellular responders of the immune system. They employ their impressive arsenal of microbicidal molecules to provide rapid and efficient defense against pathogens. However, the role of neutrophils extends far beyond microbial destruction to include tissue repair and remodeling, provision of signals to the adaptive immune system and body homeostasis. Intravital imaging has allowed the visualization of neutrophils in their native environment in both health and disease and provided crucial insights into their mechanisms of action. In the last few years the power of intravital imaging has been considerably extended by the introduction of photoconvertible proteins and intracellular signaling reporter mice. This review will highlight recent advances in our understanding of neutrophil biology based on the use of intravital microscopy to visualize their modus operandi in vivo including migration in and out of inflamed tissues, host-pathogen interactions and cell fate.

Actein Inhibits the Proliferation and Adhesion of Human Breast Cancer Cells and Suppresses Migration in vivo

Background and purpose: Metastasis is an important cause of death in breast cancer patients. Anti-metastatic agents are urgently needed since standard chemotherapeutics cannot diminish the metastatic rate. Actein, a cycloartane triterpenoid, has been demonstrated to exhibit anti-angiogenic and anti-cancer activities. Its anti-metastatic activity and underlying mechanisms were evaluated in the present study.

Methods: The effects of actein on the proliferation, cell cycle phase distribution, migration, motility and adhesion were evaluated using two human breast cancer cell lines, MDA-MB-231 (estrogen receptor-negative) and MCF-7 cells (estrogen receptor-positive) in vitro. Western blots and real-time PCR were employed to examine the protein and mRNA expression of relevant signaling pathways. A human metastatic breast cancer cell xenograft model was established in transparent zebrafish embryos to examine the anti-migration effect of actein in vivo.

Results:In vitro results showed that actein treatment significantly decreased cell proliferation, migration and motility. Furthermore, actein significantly caused G1 phase cell cycle arrest and suppressed the protein expression of matrix metalloproteinases of MDA-MB-231 cells. In addition, actein inhibited breast cancer cell adhesion to collagen, also reduced the expression of integrins. Actein treatment down-regulated the protein expression of epidermal growth factor receptor (EGFR), AKT and NF-κB signaling proteins. In vivo results demonstrated that actein (60 μM) significantly decreased the number of zebrafish embryos with migrated cells by 74% and reduced the number of migrated cells in embryos.

Conclusion: Actein exhibited anti-proliferative, anti-adhesion and anti-migration activities, with the underlying mechanisms involved the EGFR/AKT and NF-kappaB signalings. These findings shed light for the development of actein as novel anti-migration natural compound for advanced breast cancer.

Exploring the cardiac response to injury in heart transplant biopsies

BACKGROUND

Because injury is universal in organ transplantation, heart transplant endomyocardial biopsies present an opportunity to explore response to injury in heart parenchyma. Histology has limited ability to assess injury, potentially confusing it with rejection, whereas molecular changes have potential to distinguish injury from rejection. Building on previous studies of transcripts associated with T cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR), we explored transcripts reflecting injury.

METHODS

Microarray data from 889 prospectively collected endomyocardial biopsies from 454 transplant recipients at 14 centers were subjected to unsupervised principal component analysis and archetypal analysis to detect variation not explained by rejection. The resulting principal component and archetype scores were then examined for their transcript, transcript set, and pathway associations and compared to the histology diagnoses and left ventricular function.

RESULTS

Rejection was reflected by principal components PC1 and PC2, and by archetype scores S2TCMR, and S3ABMR, with S1normal indicating normalness. PC3 and a new archetype score, S4injury, identified unexplained variation correlating with expression of transcripts inducible in injury models, many expressed in macrophages and associated with inflammation in pathway analysis. S4injury scores were high in recent transplants, reflecting donation-implantation injury, and both S4injury and S2TCMR were associated with reduced left ventricular ejection fraction.

CONCLUSION

Assessment of injury is necessary for accurate estimates of rejection and for understanding heart transplant phenotypes. Biopsies with molecular injury but no molecular rejection were often misdiagnosed rejection by histology.TRAIL REGISTRATION. ClinicalTrials.gov NCT02670408FUNDING. Roche Organ Transplant Research Foundation, the University of Alberta Hospital Foundation, and Alberta Health Services.

Evaluation of collagen mixture on promoting skin wound healing in zebrafish caused by acetic acid administration

The aim of this study is to use zebrafish embryos as a quick platform for wound healing studies. At beginning, we optimized a protocol to induce skin lesion by acetic acid injection. The acetic acid injection induced regional inflammation wound hyperpigmentation by recruiting pigment cells to the wound area. Later, we applied established platform to evaluate the effect of tilapia's collagen peptide mixtures, including demonstration on promoting skin wound healing and eliminating inflammatory response. Results showed that after treating TY001, one of the above fish collagen peptide mixtures, not only repair and proliferation were induced, but also death and apoptosis cells were cleared within cutaneous lesion. Moreover, inflammatory response was suppressed along with collagen mixture treatment. Finally, the TY001-associated signaling was validated by real time-PCR, and numbers of gene associated with tissue repair and vessel proliferation were induced. To sum up, our findings provided a permissive model that may apply to generate a platform for further screening on repair and restoration technology. In addition, the tilapia fish collagen peptide mixture we applied on our model has great potential on developing clinical application on wound healing.

Cxcr1 mediates recruitment of neutrophils and supports proliferation of tumor-initiating astrocytes in vivo

Neutrophils are first-responders to sites of infection and tissue damage including the inflamed tumor microenvironment. Increasing evidence suggests that crosstalk between tumors and neutrophils can affect the progression of established tumors. However, there is a gap in our understanding of the early events that lead to neutrophil recruitment to oncogene-transformed cells and how these pathways alter tumor progression. Here, we use optically transparent zebrafish larvae to probe the early signals that mediate neutrophil recruitment to Kras-transformed astrocytes. We show that zebrafish larvae with impaired neutrophil function exhibit reduced proliferation of transformed astrocytes supporting a critical role for tumor-associated neutrophils in the early progression of tumorigenesis. Moreover, using mutants and pharmacological inhibition, we show that the chemokine receptor Cxcr1 promotes neutrophil recruitment, proliferation of tumor-initiating cells, and neoplastic mass formation. These findings highlight the power of the larval zebrafish system to image and probe early events in the tumor-initiating microenvironment and demonstrate the potential for neutrophil recruitment signaling pathways such as Cxcl8-Cxcr1 as targets for anti-cancer therapies.

Macrophages protect Talaromyces marneffei conidia from myeloperoxidase-dependent neutrophil fungicidal activity during infection establishment in vivo

Neutrophils and macrophages provide the first line of cellular defence against pathogens once physical barriers are breached, but can play very different roles for each specific pathogen. This is particularly so for fungal pathogens, which can occupy several niches in the host. We developed an infection model of talaromycosis in zebrafish embryos with the thermally-dimorphic intracellular fungal pathogen Talaromyces marneffei and used it to define different roles of neutrophils and macrophages in infection establishment. This system models opportunistic human infection prevalent in HIV-infected patients, as zebrafish embryos have intact innate immunity but, like HIV-infected talaromycosis patients, lack a functional adaptive immune system. Importantly, this new talaromycosis model permits thermal shifts not possible in mammalian models, which we show does not significantly impact on leukocyte migration, phagocytosis and function in an established Aspergillus fumigatus model. Furthermore, the optical transparency of zebrafish embryos facilitates imaging of leukocyte/pathogen interactions in vivo. Following parenteral inoculation, T. marneffei conidia were phagocytosed by both neutrophils and macrophages. Within these different leukocytes, intracellular fungal form varied, indicating that triggers in the intracellular milieu can override thermal morphological determinants. As in human talaromycosis, conidia were predominantly phagocytosed by macrophages rather than neutrophils. Macrophages provided an intracellular niche that supported yeast morphology. Despite their minor role in T. marneffei conidial phagocytosis, neutrophil numbers increased during infection from a protective CSF3-dependent granulopoietic response. By perturbing the relative abundance of neutrophils and macrophages during conidial inoculation, we demonstrate that the macrophage intracellular niche favours infection establishment by protecting conidia from a myeloperoxidase-dependent neutrophil fungicidal activity. These studies provide a new in vivo model of talaromycosis with several advantages over previous models. Our findings demonstrate that limiting T. marneffei's opportunity for macrophage parasitism and thereby enhancing this pathogen's exposure to effective neutrophil fungicidal mechanisms may represent a novel host-directed therapeutic opportunity.

A novel zebrafish intestinal tumor model reveals a role for cyp7a1-dependent tumor-liver crosstalk in causing adverse effects on the host

The nature of host organs and genes that underlie tumor-induced physiological disruption on the host remains ill-defined. Here, we establish a novel zebrafish intestinal tumor model that is suitable for addressing this issue, and find that hepatic cyp7a1, the rate-limiting factor for synthesizing bile acids [or, in the case of zebrafish, bile alcohol (BA)], is such a host gene. Inducing kras^G12D by Gal4 specifically expressed in the posterior intestine resulted in the formation of an intestinal tumor. The local intestinal tumor caused systemic detrimental effects on the host, including liver inflammation, hepatomegaly, growth defects and organismal death. Whole-organism-level gene expression analysis and metabolite measurements revealed that the intestinal tumor reduced total BA levels, possibly via altered expression of hepatic cyp7a1 Genetically overexpressing cyp7a1 in the liver restored BA synthesis and ameliorated tumor-induced liver inflammation, but not other tumor-dependent phenotypes. Thus, we found a previously unknown role of cyp7a1 as the host gene that links the intestinal tumor, hepatic cholesterol-BA metabolism and liver inflammation in tumor-bearing zebrafish larvae. Our model provides an important basis to discover host genes responsible for tumor-induced phenotypes and to uncover mechanisms underlying how tumors adversely affect host organisms.

Generation of a double binary transgenic zebrafish model to study myeloid gene regulation in response to oncogene activation in melanocytes

A complex network of inflammatory genes is closely linked to somatic cell transformation and malignant disease. Immune cells and their associated molecules are responsible for detecting and eliminating cancer cells as they establish themselves as the precursors of a tumour. By the time a patient has a detectable solid tumour, cancer cells have escaped the initial immune response mechanisms. Here, we describe the development of a double binary zebrafish model that enables regulatory programming of the myeloid cells as they respond to oncogene-activated melanocytes to be explored, focussing on the initial phase when cells become the precursors of cancer. A hormone-inducible binary system allows for temporal control of expression of different Ras oncogenes (NRasQ61K, HRasG12V and KRasG12V) in melanocytes, leading to proliferation and changes in morphology of the melanocytes. This model was coupled to binary cell-specific biotagging models allowing in vivo biotinylation and subsequent isolation of macrophage or neutrophil nuclei for regulatory profiling of their active transcriptomes. Nuclear transcriptional profiling of neutrophils, performed as they respond to the earliest precursors of melanoma in vivo, revealed an intricate landscape of regulatory factors that may promote progression to melanoma, including Serpinb1l4, Fgf1, Fgf6, Cathepsin H, Galectin 1 and Galectin 3. The model presented here provides a powerful platform to study the myeloid response to the earliest precursors of melanoma.

Discovering Macrophage Functions Using In Vivo Optical Imaging Techniques

Macrophages are an important component of host defense and inflammation and play a pivotal role in immune regulation, tissue remodeling, and metabolic regulation. Since macrophages are ubiquitous in human bodies and have versatile physiological functions, they are involved in virtually every disease, including cancer, diabetes, multiple sclerosis, and atherosclerosis. Molecular biological and histological methods have provided critical information on macrophage biology. However, many in vivo dynamic behaviors of macrophages are poorly understood and yet to be discovered. A better understanding of macrophage functions and dynamics in pathogenesis will open new opportunities for better diagnosis, prognostic assessment, and therapeutic intervention. In this article, we will review the advances in macrophage tracking and analysis with in vivo optical imaging in the context of different diseases. Moreover, this review will cover the challenges and solutions for optical imaging techniques during macrophage intravital imaging.

A Neutrophil Proteomic Signature in Surgical Trauma Wounds

Non-healing wounds continue to be a clinical challenge for patients and medical staff. These wounds have a heterogeneous etiology, including diabetes and surgical trauma wounds. It is therefore important to decipher molecular signatures that reflect the macroscopic process of wound healing. To this end, we collected wound sponge dressings routinely used in vacuum assisted therapy after surgical trauma to generate wound-derived protein profiles via global mass spectrometry. We confidently identified 311 proteins in exudates. Among them were expected targets belonging to the immunoglobulin superfamily, complement, and skin-derived proteins, such as keratins. Next to several S100 proteins, chaperones, heat shock proteins, and immune modulators, the exudates presented a number of redox proteins as well as a discrete neutrophil proteomic signature, including for example cathepsin G, elastase, myeloperoxidase, CD66c, and lipocalin 2. We mapped over 200 post-translational modifications (PTMs; cysteine/methionine oxidation, tyrosine nitration, cysteine trioxidation) to the proteomic profile, for example, in peroxiredoxin 1. Investigating manually collected exudates, we confirmed presence of neutrophils and their products, such as microparticles and fragments containing myeloperoxidase and DNA. These data confirmed known and identified less known wound proteins and their PTMs, which may serve as resource for future studies on human wound healing.

Tumor initiating cells induce Cxcr4-mediated infiltration of pro-tumoral macrophages into the brain

It is now clear that microglia and macrophages are present in brain tumors, but whether or how they affect initiation and development of tumors is not known. Exploiting the advantages of the zebrafish (Danio rerio) model, we showed that macrophages and microglia respond immediately upon oncogene activation in the brain. Overexpression of human AKT1 within neural cells of larval zebrafish led to a significant increase in the macrophage and microglia populations. By using a combination of transgenic and mutant zebrafish lines, we showed that this increase was caused by the infiltration of peripheral macrophages into the brain mediated via Sdf1b-Cxcr4b signaling. Intriguingly, confocal live imaging reveals highly dynamic interactions between macrophages/microglia and pre-neoplastic cells, which do not result in phagocytosis of pre-neoplastic cells. Finally, depletion of macrophages and microglia resulted in a significant reduction of oncogenic cell proliferation. Thus, macrophages and microglia show tumor promoting functions already during the earliest stages of the developing tumor microenvironment.

Reprofiling using a zebrafish melanoma model reveals drugs cooperating with targeted therapeutics

Phenotype-guided re-profiling of approved drug molecules presents an accelerated route to developing anticancer therapeutics by bypassing the target-identification bottleneck of target-based approaches and by sampling drugs already in the clinic. Further, combinations incorporating targeted therapies can be screened for both efficacy and toxicity. Previously we have developed an oncogenic-RAS-driven zebrafish melanoma model that we now describe display melanocyte hyperplasia while still embryos. Having devised a rapid method for quantifying melanocyte burden, we show that this phenotype can be chemically suppressed by incubating V12RAS transgenic embryos with potent and selective small molecule inhibitors of either MEK or PI3K/mTOR. Moreover, we demonstrate that combining MEK inhibitors (MEKi) with dual PI3K/mTOR inhibitors (PI3K/mTORi) resulted in a super-additive suppression of melanocyte hyperplasia. The robustness and simplicity of our novel screening assay inspired us to perform a modest screen of FDA approved compounds for their ability to potentiate MEKi PD184352 or PI3K/mTORi NVPBEZ235 suppression of V12RAS-driven melanocyte hyperplasia. Through this route, we confirmed Rapamycin as a compound that could synergize with MEKi and even more so with PI3K/mTORi to suppress melanoma development, including suppressing the growth of cultured human melanoma cells. Further, we discovered two additional compounds-Disulfiram and Tanshinone-that also co-operate with MEKi to suppress the growth of transformed zebrafish melanocytes and showed activity toward cultured human melanoma cells. In conclusion, we provide proof-of-concept that our phenotype-guided screen could be used to identify compounds that affect melanoma development and prompt further evaluation of Disulfiram and Tanshinone as possible partners for combination therapy.

Macrophage-Dependent Cytoplasmic Transfer during Melanoma Invasion In Vivo

Interactions between tumor cells and tumor-associated macrophages play critical roles in the initiation of tumor cell motility. To capture the cellular interactions of the tumor microenvironment with high-resolution imaging, we directly visualized tumor cells and their interactions with macrophages in zebrafish. Live imaging in zebrafish revealed that macrophages are dynamic, yet maintain sustained contact with tumor cells. In addition, the recruitment of macrophages to tumor cells promotes tumor cell dissemination. Using a Cre/LoxP strategy, we found that macrophages transfer cytoplasm to tumor cells in zebrafish and mouse models. Remarkably, macrophage cytoplasmic transfer correlated with melanoma cell dissemination. We further found that macrophages transfer cytoplasm to tumor cells upon cell contact in vitro. Thus, we present a model in which macrophage/tumor cell contact allows for the transfer of cytoplasmic molecules from macrophages to tumor cells corresponding to increased tumor cell motility and dissemination.

Adoption of in vitro systems and zebrafish embryos as alternative models for reducing rodent use in assessments of immunological and oxidative stress responses to nanomaterials

Assessing the safety of engineered nanomaterials (NMs) is paramount to the responsible and sustainable development of nanotechnology, which provides huge societal benefits. Currently, there is no evidence that engineered NMs cause detrimental health effects in humans. However, investigation of NM toxicity using in vivo, in vitro, in chemico, and in silico models has demonstrated that some NMs stimulate oxidative stress and inflammation, which may lead to adverse health effects. Accordingly, investigation of these responses currently dominates NM safety assessments. There is a need to reduce reliance on rodent testing in nanotoxicology for ethical, financial and legislative reasons, and due to evidence that rodent models do not always predict the human response. We advocate that in vitro models and zebrafish embryos should have greater prominence in screening for NM safety, to better align nanotoxicology with the 3Rs principles. Zebrafish are accepted for use by regulatory agencies in chemical safety assessments (e.g. developmental biology) and there is growing acceptance of their use in biomedical research, providing strong foundations for their use in nanotoxicology. We suggest that investigation of the response of phagocytic cells (e.g. neutrophils, macrophages) in vitro should also form a key part of NM safety assessments, due to their prominent role in the first line of defense. The development of a tiered testing strategy for NM hazard assessment that promotes the more widespread adoption of non-rodent, alternative models and focuses on investigation of inflammation and oxidative stress could make nanotoxicology testing more ethical, relevant, and cost and time efficient.

Distinct effects of inflammation on preconditioning and regeneration of the adult zebrafish heart

The adult heart is able to activate cardioprotective programmes and modifies its architecture in response to physiological or pathological changes. While mammalian cardiac remodelling often involves hypertrophic expansion, the adult zebrafish heart exploits hyperplastic growth. This capacity depends on the responsiveness of zebrafish cardiomyocytes to mitogenic signals throughout their entire life. Here, we have examined the role of inflammation on the stimulation of cell cycle activity in the context of heart preconditioning and regeneration. We used thoracotomy as a cardiac preconditioning model and cryoinjury as a model of cardiac infarction in the adult zebrafish. First, we performed a spatio-temporal characterization of leucocytes and cycling cardiac cells after thoracotomy. This analysis revealed a concomitance between the infiltration of inflammatory cells and the stimulation of the mitotic activity. However, decreasing the immune response using clodronate liposome injection, PLX3397 treatment or anti-inflammatory drugs surprisingly had no effect on the re-entry of cardiac cells into the cell cycle. In contrast, reducing inflammation using the same strategies after cryoinjury strongly impaired cardiac cell mitotic activity and the regenerative process. Taken together, our results show that, while the immune response is not necessary to induce cell-cycle activity in intact preconditioned hearts, inflammation is required for the regeneration of injured hearts in zebrafish.

Quo natas, Danio?-Recent Progress in Modeling Cancer in Zebrafish

Over the last decade, zebrafish has proven to be a powerful model in cancer research. Zebrafish form tumors that histologically and genetically resemble human cancers. The live imaging and cost-effective compound screening possible with zebrafish especially complement classic mouse cancer models. Here, we report recent progress in the field, including genetically engineered zebrafish cancer models, xenotransplantation of human cancer cells into zebrafish, promising approaches toward live investigation of the tumor microenvironment, and identification of therapeutic strategies by performing compound screens on zebrafish cancer models. Given the recent advances in genome editing, personalized zebrafish cancer models are now a realistic possibility. In addition, ongoing automation will soon allow high-throughput compound screening using zebrafish cancer models to be part of preclinical precision medicine approaches.

Wnt signaling controls pro-regenerative Collagen XII in functional spinal cord regeneration in zebrafish

The inhibitory extracellular matrix in a spinal lesion site is a major impediment to axonal regeneration in mammals. In contrast, the extracellular matrix in zebrafish allows substantial axon re-growth, leading to recovery of movement. However, little is known about regulation and composition of the growth-promoting extracellular matrix. Here we demonstrate that activity of the Wnt/β-catenin pathway in fibroblast-like cells in the lesion site is pivotal for axon re-growth and functional recovery. Wnt/β-catenin signaling induces expression of col12a1a/b and deposition of Collagen XII, which is necessary for axons to actively navigate the non-neural lesion site environment. Overexpression of col12a1a rescues the effects of Wnt/β-catenin pathway inhibition and is sufficient to accelerate regeneration. We demonstrate that in a vertebrate of high regenerative capacity, Wnt/β-catenin signaling controls the composition of the lesion site extracellular matrix and we identify Collagen XII as a promoter of axonal regeneration. These findings imply that the Wnt/β-catenin pathway and Collagen XII may be targets for extracellular matrix manipulations in non-regenerating species.

Following spinal injury in zebrafish, non-neural cells establish an extracellular matrix to promote axon re-growth but how this is regulated is unclear. Here, the authors show that Wnt/β-catenin signaling in fibroblast-like cells at a lesion activates axon re-growth via deposition of Collagen XII.

Neutrophil swarming: an essential process of the neutrophil tissue response

Neutrophil infiltration into inflamed and infected tissues is a fundamental process of the innate immune response. While neutrophil interactions with the blood vessel wall have been intensely studied over the last decades, neutrophil dynamics beyond the vasculature have for a long time remained poorly investigated. Recent intravital microscopy studies of neutrophil populations directly at the site of tissue damage or microbial invasion have changed our perspective on neutrophil responses within tissues. Swarm-like migration patterns of neutrophils, referred to as 'neutrophil swarming', have been detected in diverse tissues under conditions of sterile inflammation and infection with various pathogens, including bacteria, fungi, and parasites. Current work has begun to unravel the molecular pathways choreographing the sequential phases of highly coordinated chemotaxis followed by neutrophil accumulation and the formation of substantial neutrophil clusters. It is now clear that intercellular communication among neutrophils amplifies their recruitment in a feed-forward manner, which provides them with a level of self-organization during neutrophil swarming. This review will summarize recent developments and current concepts on neutrophil swarming, an important process of the neutrophil tissue response with a critical role in maintaining the balance between host protection and inflammation-driven tissue destruction.

Macrophages, but not neutrophils, are critical for proliferation of Burkholderia cenocepacia and ensuing host-damaging inflammation

Bacteria of the Burkholderia cepacia complex (Bcc) can cause devastating pulmonary infections in cystic fibrosis (CF) patients, yet the precise mechanisms underlying inflammation, recurrent exacerbations and transition from chronic stages to acute infection and septicemia are not known. Bcc bacteria are generally believed to have a predominant extracellular biofilm life style in infected CF lungs, similar to Pseudomonas aeruginosa, but this has been challenged by clinical observations which show Bcc bacteria predominantly in macrophages. More recently, Bcc bacteria have emerged in nosocomial infections of patients hospitalized for reasons unrelated to CF. Research has abundantly shown that Bcc bacteria can survive and replicate in mammalian cells in vitro, yet the importance of an intracellular life style during infection in humans is unknown. Here we studied the contribution of innate immune cell types to fatal pro-inflammatory infection caused by B. cenocepacia using zebrafish larvae. In strong contrast to the usual protective role for macrophages against microbes, our results show that these phagocytes significantly worsen disease outcome. We provide new insight that macrophages are critical for multiplication of B. cenocepacia in the host and for development of a fatal, pro-inflammatory response that partially depends on Il1-signalling. In contrast, neutrophils did not significantly contribute to disease outcome. In subcutaneous infections that are dominated by neutrophil-driven phagocytosis, the absence of a functional NADPH oxidase complex resulted in a small but measurably higher increase in bacterial growth suggesting the oxidative burst helps limit bacterial multiplication; however, neutrophils were unable to clear the bacteria. We suggest that paradigm-changing approaches are needed for development of novel antimicrobials to efficiently disarm intracellular bacteria of this group of highly persistent, opportunistic pathogens.

Macrophage Functions in Tissue Patterning and Disease: New Insights from the Fly

Macrophages are multifunctional innate immune cells that seed all tissues within the body and play disparate roles throughout development and in adult tissues, both in health and disease. Their complex developmental origins and many of their functions are being deciphered in mammalian tissues, but opportunities for live imaging and the genetic tractability of Drosophila are offering complementary insights into how these fascinating cells integrate a multitude of guidance cues to fulfill their many tasks and migrate to distant sites to either direct developmental patterning or raise an inflammatory response.

Wound-induced Ca2+ wave propagates through a simple release and diffusion mechanism

Damage-associated molecular patterns (DAMPs) are critical mediators of information concerning tissue damage from damaged cells to neighboring healthy cells. ATP acts as an effective DAMP when released into extracellular space from damaged cells. Extracellular ATP receptors monitor tissue damage and activate a Ca²⁺ wave in the surrounding healthy cells. How the Ca²⁺ wave propagates through cells after a wound is unclear. Ca²⁺ wave activation can occur extracellularly via external receptors or intracellularly through GAP junctions. Three potential mechanisms to propagate the Ca²⁺ wave are source and sink, amplifying wave, and release and diffusion. Both source and sink and amplifying wave regulate ATP levels using hydrolysis or secretion, respectively, whereas release and diffusion relies on dilution. Here we systematically test these hypotheses using a microfluidics assay to mechanically wound an epithelial monolayer in combination with direct manipulation of ATP hydrolysis and release. We show that a release and diffusion model sufficiently explains Ca²⁺-wave propagation after an epithelial wound. A release and diffusion model combines the benefits of fast activation at short length scales with a self-limiting response to prevent unnecessary inflammatory responses harmful to the organism.

In Vivo Imaging Sheds Light on Immune Cell Migration and Function in Cancer

There is ample evidence for both beneficial and harmful involvement of the immune system in tumor development and spread. Immune cell recruitment to tumors is essential not only for the success of anticancer immune therapies but also for tumor-induced immune suppression. Now that immune-based therapies are playing an increasingly important role in treatment of solid tumors such as metastatic melanomas, precise analysis of the in vivo contributions of different leukocyte subsets in tumor immunity has become an even greater priority. Recently, this goal has been markedly facilitated by the use of intravital microscopy, which has enabled us to visualize the dynamic interactions between cells of the immune system and tumor targets in the context of the tumor microenvironment. For example, intravital imaging techniques have shed new light on T cell infiltration of tumors, the mechanisms of cancer cell killing, and how myeloid cells contribute to tumor tolerance and spread. This mini-review summarizes the recent advances made to our understanding of the roles of innate and adaptive immune cells in cancer based on the use of these in vivo imaging approaches.

Bystander cells enhance NK cytotoxic efficiency by reducing search time

Natural killer (NK) cells play a central role during innate immune responses by eliminating pathogen-infected or tumorigenic cells. In the microenvironment, NK cells encounter not only target cells but also other cell types including non-target bystander cells. The impact of bystander cells on NK killing efficiency is, however, still elusive. In this study we show that the presence of bystander cells, such as P815, monocytes or HUVEC, enhances NK killing efficiency. With bystander cells present, the velocity and persistence of NK cells were increased, whereas the degranulation of lytic granules remained unchanged. Bystander cell-derived H2O2 was found to mediate the acceleration of NK cell migration. Using mathematical diffusion models, we confirm that local acceleration of NK cells in the vicinity of bystander cells reduces their search time to locate target cells. In addition, we found that integrin β chains (β1, β2 and β7) on NK cells are required for bystander-enhanced NK migration persistence. In conclusion, we show that acceleration of NK cell migration in the vicinity of H2O2-producing bystander cells reduces target cell search time and enhances NK killing efficiency.

Tumor immunology viewed from alternative animal models-the Xenopus story

A PURPOSE OF REVIEW

Nonmammalian comparative animal models are important not only to gain fundamental evolutionary understanding of the complex interactions of tumors with the immune system, but also to better predict the applicability of novel immunotherapeutic approaches to humans. After reviewing recent advances in developing alternative models, we focus on the amphibian Xenopus laevis and its usefulness in deciphering the perplexing roles of MHC class I-like molecules and innate (i)T cells in tumor immunity.

B RECENT FINDINGS

Experiments using MHC-defined inbred and cloned animals, tumor cell lines, effective reagents, sequenced genomes, and adapted gene editing techniques in Xenopus, have revealed that the critical involvement of class I-like molecules and iT cells in tumor immunity has been conserved during evolution.

C SUMMARY

Comparative studies with the X. laevis tumor immunity model can contribute to the development of better and more efficient cancer immunotherapies.

Live imaging the earliest host innate immune response to preneoplastic cells using a zebrafish inducible KalTA4-ERT2/UAS system

As cancers develop, transformed cells hijack various host mechanisms and manipulate them to create a dynamic tumor microenvironment, which supports tumor growth. This protumorigenic microenvironment is made up of many different cell types, including transformed cells, fibroblasts, inflammatory cells, and endothelial cells, the interactions of which have been shown to play a role in sustaining tumor growth. Multiple reports implicate the inflammatory cells of the tumor microenvironment as having both pro- and antitumorigenic roles, the balance of which is vital for the progression of the tumor, and while our understanding of established cancers has vastly increased since the turn of the 21st Century, our knowledge of these cellular interactions at the earliest stages of cancer initiation and development remains relatively limited. This is largely due to difficulties in monitoring these processes in vivo and in real time. Since the late nineties, the zebrafish (Danio rerio) has emerged as a vital model organism, allowing studies of previously unattainable stages of tumor initiation in a vertebrate model system. Using genetic and live-imaging approaches, this model system can be used both independently to monitor stages of tumor progression from the earliest initiation stages and incorporated into previously established systems to investigate the interactions between cancer cells and the various cell types of the tumor microenvironment, including inflammatory cells. Here, we describe the use of an inducible KalTA4-ER^T2/UAS expression system in zebrafish, which allows spatial and temporal control of preneoplastic cell (PNC) growth and monitoring of innate immune cells in response to the developing PNC microenvironment.

Investigating microglia-brain tumor cell interactions in vivo in the larval zebrafish brain

Glioblastoma is the most frequent and aggressive primary malignant brain tumor. Gliomas exhibit high genetic diversity in addition to complex and variable clinical features. Glioblastoma tumors are highly resistant to multimodal therapies and there is significant patient mortality within the first two years after prognosis. At present clinical treatments are palliative, not curative. Glioblastomas contain a high number of microglia and infiltrating macrophages, which are positively correlated with glioma grade and invasiveness. Microglia are the resident macrophages of the central nervous system. These cells constantly scan the brain and react promptly to any abnormality, removing detrimental factors and safeguarding the central nervous system against further damage. Microglia and macrophages that have colonized the glioblastoma display protumoral functions and promote tumor growth. The optically transparent zebrafish larva facilitates imaging of fluorescently labeled cells at high spatial and temporal resolution in vivo. It is therefore an excellent model to investigate microglia-glioma cell interactions at the early stages of tumor development. Here we provide several methods that can be used to study the early stages of microglia-glioma cell interactions in the zebrafish. We present a technique for the xenotransplantation of mammalian oncogenic cells into the zebrafish brain and provide advice for image capture and analysis.

Collaboration of cancer-associated fibroblasts and tumour-associated macrophages for neuroblastoma development

Neuroblastoma is the most common extracranial solid tumour in children and is histologically classified by its Schwannian stromal cells. Although having fewer Schwannian stromal cells is generally associated with more aggressive phenotypes, the exact roles of other stromal cells (mainly macrophages and fibroblasts) are unclear. Here, we examined 41 cases of neuroblastoma using immunohistochemistry for the tumour-associated macrophage (TAM) markers CD68, CD163, and CD204, and a cancer-associated fibroblast (CAF) marker, alpha smooth muscle actin (αSMA). Each case was assigned to low/high groups on the basis of the number of TAMs or three groups on the basis of the αSMA-staining area for CAFs. Both the number of TAMs and the area of CAFs were significantly correlated with clinical stage, MYCN amplification, bone marrow metastasis, histological classification, histological type, and risk classification. Furthermore, TAM settled in the vicinity of the CAF area, suggesting their close interaction within the tumour microenvironment. We next determined the effects of conditioned medium of a neuroblastoma cell line (NBCM) on bone marrow-derived mesenchymal stem cells (BM-MSCs) and peripheral blood mononuclear cell (PBMC)-derived macrophages in vitro. The TAM markers CD163 and CD204 were significantly up-regulated in PBMC-derived macrophages treated with NBCM. The expression of αSMA by BM-MSCs was increased in NBCM-treated cells. Co-culturing with CAF-like BM-MSCs did not enhance the invasive ability but supported the proliferation of tumour cells, whereas tumour cells co-cultured with TAM-like macrophages had the opposite effect. Intriguingly, TAM-like macrophages enhanced not only the invasive abilities of tumour cells and BM-MSCs but also the proliferation of BM-MSCs. CXCL2 secreted from TAM-like macrophages plays an important role in tumour invasiveness. Taken together, these results indicate that PBMC-derived macrophages and BM-MSCs are recruited to a tumour site and activated into TAMs and CAFs, respectively, followed by the formation of favourable environments for neuroblastoma progression. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Imaging Cancer Angiogenesis and Metastasis in a Zebrafish Embryo Model

Tumor angiogenesis and metastasis are key steps of cancer progression. In vitro and animal model studies have contributed to partially elucidating the mechanisms involved in these processes and in developing therapies. Besides the improvements in fundamental research and the optimization of therapeutic regimes, cancer still remains a major health threatening condition and therefore the development of new models is needed. The zebrafish is a powerful tool to study tumor angiogenesis and metastasis, because it allows the visualization of fluorescently labelled tumor cells inducing vessel remodeling, disseminating and invading surrounding tissues in a whole transparent embryo. The embryo model has also been used to address the contribution of the tumor stroma in sustaining tumor angiogenesis and spreading. Simultaneously, new anti-angiogenic drugs and compounds affecting malignant cell survival and migration can be tested by simply adding the compound into the water of living embryos. Therefore the zebrafish model offers the opportunity to gain more knowledge on cancer angiogenesis and metastasis in vivo with the final aim of providing new translational insights into therapeutic approaches to help patients.

Zebrafish fin regeneration after cryoinjury-induced tissue damage

Although fin regeneration following an amputation procedure has been well characterized, little is known about the impact of prolonged tissue damage on the execution of the regenerative programme in the zebrafish appendages. To induce histolytic processes in the caudal fin, we developed a new cryolesion model that combines the detrimental effects of freezing/thawing and ischemia. In contrast to the common transection model, the damaged part of the fin was spontaneously shed within two days after cryoinjury. The remaining stump contained a distorted margin with a mixture of dead material and healthy cells that concomitantly induced two opposing processes of tissue debris degradation and cellular proliferation, respectively. Between two and seven days after cryoinjury, this reparative/proliferative phase was morphologically featured by displaced fragments of broken bones. A blastemal marker msxB was induced in the intact mesenchyme below the damaged stump margin. Live imaging of epithelial and osteoblastic transgenic reporter lines revealed that the tissue-specific regenerative programmes were initiated after the clearance of damaged material. Despite histolytic perturbation during the first week after cryoinjury, the fin regeneration resumed and was completed without further alteration in comparison to the simple amputation model. This model reveals the powerful ability of the zebrafish to restore the original appendage architecture after the extended histolysis of the stump.

Summary: Fin cryolesion resulted in histolysis and a delayed tissue loss. Despite prolonged destruction of the stump architecture, fin regeneration resumed and was normally completed, revealing robustness of the regenerative capacity.

Melanosomes in pigmented epithelia maintain eye lens transparency during zebrafish embryonic development

Altered levels of trace elements are associated with increased oxidative stress that is eventually responsible for pathologic conditions. Oxidative stress has been proposed to be involved in eye diseases, including cataract formation. We visualized the distribution of metals and other trace elements in the eye of zebrafish embryos by micro X-ray fluorescence (μ-XRF) imaging. Many elements showed highest accumulation in the retinal pigment epithelium (RPE) of the zebrafish embryo. Knockdown of the zebrafish brown locus homologues tyrp1a/b eliminated accumulation of these elements in the RPE, indicating that they are bound by mature melanosomes. Furthermore, albino (slc45a2) mutants, which completely lack melanosomes, developed abnormal lens reflections similar to the congenital cataract caused by mutation of the myosin chaperon Unc45b, and an in situ spin trapping assay revealed increased oxidative stress in the lens of albino mutants. Finally transplanting a wildtype lens into an albino mutant background resulted in cataract formation. These data suggest that melanosomes in pigment epithelial cells protect the lens from oxidative stress during embryonic development, likely by buffering trace elements.

Neutrophils: Critical components in experimental animal models of cancer

Neutrophils have a crucial role in tumor development and metastatic progression. The contribution of neutrophils in tumor development is multifaceted and contradictory. On the one hand, neutrophils prompt tumor inception, promote tumor development by mediating the initial angiogenic switch and facilitate colonization of circulating tumor cells, and on the other hand, have cytotoxic and anti-metastatic capabilities. Our understanding of the role of neutrophils in tumor development has greatly depended on different experimental animal models of cancer. In this review we cover important findings that have been made about neutrophils in experimental animal models of cancer, point to their advantages and limitations, and discuss novel techniques that can be used to expand our knowledge of how neutrophils influence tumor progression.

Spinal motor neurons are regenerated after mechanical lesion and genetic ablation in larval zebrafish

In adult zebrafish, relatively quiescent progenitor cells show lesion-induced generation of motor neurons. Developmental motor neuron generation from the spinal motor neuron progenitor domain (pMN) sharply declines at 48 hours post-fertilisation (hpf). After that, mostly oligodendrocytes are generated from the same domain. We demonstrate here that within 48 h of a spinal lesion or specific genetic ablation of motor neurons at 72 hpf, the pMN domain reverts to motor neuron generation at the expense of oligodendrogenesis. By contrast, generation of dorsal Pax2-positive interneurons was not altered. Larval motor neuron regeneration can be boosted by dopaminergic drugs, similar to adult regeneration. We use larval lesions to show that pharmacological suppression of the cellular response of the innate immune system inhibits motor neuron regeneration. Hence, we have established a rapid larval regeneration paradigm. Either mechanical lesions or motor neuron ablation is sufficient to reveal a high degree of developmental flexibility of pMN progenitor cells. In addition, we show an important influence of the immune system on motor neuron regeneration from these progenitor cells.

NADPH oxidases in oxidant production by microglia: activating receptors, pharmacology and association with disease

Microglia are the resident immune cells of the CNS and constitute a self-sustaining population of CNS-adapted tissue macrophages. As mononuclear phagocytic cells, they express high levels of superoxide-producing NADPH oxidases (NOX). The sole function of the members of the NOX family is to generate reactive oxygen species (ROS) that are believed to be important in CNS host defence and in the redox signalling circuits that shape the different activation phenotypes of microglia. NOX are also important in pathological conditions, where over-generation of ROS contributes to neuronal loss via direct oxidative tissue damage or disruption of redox signalling circuits. In this review, we assess the evidence for involvement of NOX in CNS physiopathology, with particular emphasis on the most important surface receptors that lead to generation of NOX-derived ROS. We evaluate the potential significance of the subcellular distribution of NOX isoforms for redox signalling or release of ROS to the extracellular medium. Inhibitory mechanisms that have been reported to restrain NOX activity in microglia and macrophages in vivo are also discussed. We provide a critical appraisal of frequently used and recently developed NOX inhibitors. Finally, we review the recent literature on NOX and other sources of ROS that are involved in activation of the inflammasome and discuss the potential influence of microglia-derived oxidants on neurogenesis, neural differentiation and culling of surplus progenitor cells. The degree to which excessive, badly timed or misplaced NOX activation in microglia may affect neuronal homeostasis in physiological or pathological conditions certainly merits further investigation.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Cross-species models of human melanoma

Although transformation of melanocytes to melanoma is rare, the rapid growth, systemic spread, as well as the chemoresistance of melanoma present significant challenges for patient care. Here we review animal models of melanoma, including murine, canine, equine, and zebrafish models, and detail the immense contribution these models have made to our knowledge of human melanoma development, and to melanocyte biology. We also highlight the opportunities for cross-species comparative genomic studies of melanoma to identify the key molecular events that drive this complex disease.

In Vivo Imaging of Cancer in Zebrafish

Zebrafish cancer models have greatly advanced our understanding of malignancy in humans. This is made possible due to the unique advantages of the zebrafish model including ex vivo development and large clutch sizes, which enable large-scale genetic and chemical screens. Transparency of the embryo and the creation of adult zebrafish devoid of pigmentation (casper) have permitted unprecedented ability to dynamically visualize cancer progression in live animals. When coupled with fluorescent reporters and transgenic approaches that drive oncogenesis, it is now possible to label entire or subpopulations of cancer cells and follow cancer growth in near real-time. Here, we will highlight aspects of in vivo imaging using the zebrafish and how it has enhanced our understanding of the fundamental aspects of tumor initiation, self-renewal, neovascularization, tumor cell heterogeneity, invasion and metastasis. Importantly, we will highlight the contribution of cancer imaging in zebrafish for drug discovery.

Focusing the Spotlight on the Zebrafish Intestine to Illuminate Mechanisms of Colorectal Cancer

Colorectal cancer, encompassing colon and rectal cancer, arises from the epithelial lining of the large bowel. It is most prevalent in Westernised societies and is increasing in frequency as the world becomes more industrialised. Unfortunately, metastatic colorectal cancer is not cured by chemotherapy and the annual number of deaths caused by colorectal cancer, currently 700,000, is expected to rise. Our understanding of the contribution that genetic mutations make to colorectal cancer, although incomplete, is reasonably well advanced. However, it has only recently become widely appreciated that in addition to the ongoing accumulation of genetic mutations, chronic inflammation also plays a critical role in the initiation and progression of this disease. While a robust and tractable genetic model of colorectal cancer in zebrafish, suitable for pre-clinical studies, is not yet available, the identification of genes required for the rapid proliferation of zebrafish intestinal epithelial cells during development has highlighted a number of essential genes that could be targeted to disable colorectal cancer cells. Moreover, appreciation of the utility of zebrafish to study intestinal inflammation is on the rise. In particular, zebrafish provide unique opportunities to investigate the impact of genetic and environmental factors on the integrity of intestinal epithelial barrier function. With currently available tools, the interplay between epigenetic regulators, intestinal injury, microbiota composition and innate immune cell mobilisation can be analysed in exquisite detail. This provides excellent opportunities to define critical events that could potentially be targeted therapeutically. Further into the future, the use of zebrafish larvae as hosts for xenografts of human colorectal cancer tissue, while still in its infancy, holds great promise that zebrafish could one day provide a practical, preclinical personalized medicine platform for the rapid assessment of the metastatic potential and drug-sensitivity of patient-derived cancers.

Imaging of Human Cancer Cell Proliferation, Invasion, and Micrometastasis in a Zebrafish Xenogeneic Engraftment Model

The xenograft model, using the early life stages of the zebrafish, allows imaging of tumor cell behavior both on a single cell and whole organism level, over time, within a week. This robust and reproducible assay can be used as an intermediate step between in vitro techniques and the expensive, and time consuming, murine models of cancer invasion and metastasis.In this chapter, a detailed protocol to inject human cancer cells into the blood circulation of a zebrafish embryo is described; the engraftment procedure is then followed by visualization and quantification methods of tumor cell proliferation, invasion, and micrometastasis formation during subsequent larval development. Interaction with the host microenvironment is also considered.

Neutrophils in the Tumor Microenvironment

Neutrophils are the first responders to sites of acute tissue damage and infection. Recent studies suggest that in addition to neutrophil apoptosis, resolution of neutrophil inflammation at wounds can be mediated by reverse migration from tissues and transmigration back into the vasculature. In settings of chronic inflammation, neutrophils persist in tissues, and this persistence has been associated with cancer progression. However, the role of neutrophils in the tumor microenvironment remains controversial, with evidence for both pro- and anti-tumor roles. Here we review the mechanisms that regulate neutrophil recruitment and resolution at sites of tissue damage, with a specific focus on the tumor microenvironment. We discuss the current understanding as to how neutrophils alter the tumor microenvironment to support or hinder cancer progression, and in this context outline gaps in understanding and important areas of inquiry.

Neutrophils, wounds, and cancer progression

Chronic inflammation is associated with tumorigenesis, but how acute inflammation affects the tumor microenvironment is less known. Recently, Antonio et al. (2015) found that neutrophils attracted to an acute wound such as a biopsy drive cell proliferation of nearby pre-neoplastic cells, suggesting that acute wounds may promote cancer progression.

Hydrogen peroxide - production, fate and role in redox signaling of tumor cells

Hydrogen peroxide (H₂O₂) is involved in various signal transduction pathways and cell fate decisions. The mechanism of the so called “redox signaling” includes the H₂O₂-mediated reversible oxidation of redox sensitive cysteine residues in enzymes and transcription factors thereby altering their activities. Depending on its intracellular concentration and localization, H₂O₂ exhibits either pro- or anti-apoptotic activities. In comparison to normal cells, cancer cells are characterized by an increased H₂O₂ production rate and an impaired redox balance thereby affecting the microenvironment as well as the anti-tumoral immune response. This article reviews the current knowledge about the intracellular production of H₂O₂ along with redox signaling pathways mediating either the growth or apoptosis of tumor cells. In addition it will be discussed how the targeting of H₂O₂-linked sources and/or signaling components involved in tumor progression and survival might lead to novel therapeutic targets.

Tumors: wounds that do not heal-redux

Similarities between tumors and the inflammatory response associated with wound healing have been recognized for more than 150 years and continue to intrigue. Some years ago, based on our then recent discovery of vascular permeability factor (VPF)/VEGF, I suggested that tumors behaved as wounds that do not heal. More particularly, I proposed that tumors co-opted the wound-healing response to induce the stroma they required for maintenance and growth. Work over the past few decades has supported this hypothesis and has put it on a firmer molecular basis. In outline, VPF/VEGF initiates a sequence of events in both tumors and wounds that includes the following: increased vascular permeability; extravasation of plasma, fibrinogen and other plasma proteins; activation of the clotting system outside the vascular system; deposition of an extravascular fibrin gel that serves as a provisional stroma and a favorable matrix for cell migration; induction of angiogenesis and arterio-venogenesis; subsequent degradation of fibrin and its replacement by "granulation tissue" (highly vascular connective tissue); and, finally, vascular resorption and collagen synthesis, resulting in the formation of dense fibrous connective tissue (called "scar tissue" in wounds and "desmoplasia" in cancer). A similar sequence of events also takes place in a variety of important inflammatory diseases that involve cellular immunity.

The wound inflammatory response exacerbates growth of pre-neoplastic cells and progression to cancer

There is a long-standing association between wound healing and cancer, with cancer often described as a "wound that does not heal". However, little is known about how wounding, such as following surgery, biopsy collection or ulceration, might impact on cancer progression. Here, we use a translucent zebrafish larval model of Ras(G12V)-driven neoplasia to image the interactions between inflammatory cells drawn to a wound, and to adjacent pre-neoplastic cells. We show that neutrophils are rapidly diverted from a wound to pre-neoplastic cells and these interactions lead to increased proliferation of the pre-neoplastic cells. One of the wound-inflammation-induced trophic signals is prostaglandin E2 (PGE2). In an adult model of chronic wounding in zebrafish, we show that repeated wounding with subsequent inflammation leads to a greater incidence of local melanoma formation. Our zebrafish studies led us to investigate the innate immune cell associations in ulcerated melanomas in human patients. We find a strong correlation between neutrophil presence at sites of melanoma ulceration and cell proliferation at these sites, which is associated with poor prognostic outcome.

Imaging innate immune responses at tumour initiation: new insights from fish and flies

Recent imaging studies in genetically tractable and translucent zebrafish and Drosophila melanogaster models have opened a window on the earliest stages of tumorigenesis, when pre-neoplastic cells first arise in tissues before they progress into full-blown cancers. Innate immune cells often find these cells soon after they develop, but this efficient surveillance is not always good for the host because although immune cells have phagocytic capacity, they can also nurture the growing clones of pre-neoplastic cells. We describe these newly observed early interactions between immune cells and cancer cells and speculate on their potential clinical implications.

Tumor microenvironment tenascin-C promotes glioblastoma invasion and negatively regulates tumor proliferation

BACKGROUND

Glioblastoma (GBM) is the most frequent and aggressive primary brain tumor in adults. Recent research on cancer stroma indicates that the brain microenvironment plays a substantial role in tumor malignancy and treatment responses to current antitumor therapy. In this work, we have investigated the effect of alterations in brain tumor extracellular matrix tenascin-C (TNC) on brain tumor growth patterns including proliferation and invasion.

METHODS

Since intracranial xenografts from patient-derived GBM neurospheres form highly invasive tumors that recapitulate the invasive features demonstrated in human patients diagnosed with GBM, we studied TNC gain-of-function and loss-of function in these GBM neurospheres in vitro and in vivo.

RESULTS

TNC loss-of-function promoted GBM neurosphere cell adhesion and actin cytoskeleton organization. Yet, TNC loss-of-function or exogenous TNC had no effect on GBM neurosphere cell growth in vitro. In animal models, decreased TNC in the tumor microenvironment was accompanied by decreased tumor invasion and increased tumor proliferation, suggesting that TNC regulates the "go-or-grow" phenotypic switch of glioma in vivo. We demonstrated that decreased TNC in the tumor microenvironment modulated behaviors of stromal cells including endothelial cells and microglia, resulting in enlarged tumor blood vessels and activated microglia in tumors. We further demonstrated that tumor cells with decreased TNC expression are sensitive to anti-proliferative treatment in vitro.

CONCLUSION

Our findings suggest that detailed understanding of how TNC in the tumor microenvironment influences tumor behavior and the interactions between tumor cells and surrounding nontumor cells will benefit novel combinatory antitumor strategies to treat malignant brain tumors.

Stimulation of hepatocarcinogenesis by neutrophils upon induction of oncogenic kras expression in transgenic zebrafish

BACKGROUND & AIMS

Chronic inflammation is a major etiological factor for hepatocellular carcinoma (HCC), but how immune cells respond in the initiation of hepatocarcinogenesis remains uncharacterized. This study aims to investigate the response and roles of neutrophils in early hepatocarcinogenesis.

METHODS

By inducible expression of oncogenic kras(V12) in hepatocytes in transgenic zebrafish combined with live imaging of neutrophils in transparent larvae, the response of neutrophils to oncogenic liver was characterized and their roles investigated by pharmaceutical and genetic manipulations.

RESULTS

We found a rapid recruitment of neutrophils to the liver upon induction of kras(V12) expression. Pharmaceutical stimulation of neutrophils resulted in further increases of neutrophils in oncogenic livers, liver size and tumor severity, while inhibition of neutrophils caused decreases of liver-associated neutrophils and liver size. Time-lapse video indicated that neutrophils had a stagnant migratory pattern meandering along the tumor edge but became relatively stationary upon entering the kras(V12)-expressing liver. Both oncogenic hepatocytes and tumor-associated neutrophils (TANs) were isolated via fluorescence-activated cell sorting. Molecular analyses indicated a pro-inflammatory microenvironment, as marked by increased tgfβ1a expression in kras(V12)-expressing hepatocytes and a loss of anti-tumor activities in TANs. Depletion of Tgf-β significantly reduced the number of TANs and the size of oncogenic liver.

CONCLUSIONS

An inflammatory cue from oncogenic hepatocytes upon induction of kras(V12) expression causes a rapid recruitment of neutrophils to oncogenic liver and the neutrophils play a promoting role in early hepatocarcinogenesis.