Hif-1α-Induced Expression of Il-1β Protects against Mycobacterial Infection in Zebrafish

The Janus face of HIF-1α in ischemic stroke and the possible associated pathways

Stroke is the most devastating disease, causing paralysis and eventually death. Many clinical and experimental trials have been done in search of a new safe and efficient medicine; nevertheless, scientists have yet to discover successful remedies that are also free of adverse effects. This is owing to the variability in intensity, localization, medication routes, and each patient's immune system reaction. HIF-1α represents the modern tool employed to treat stroke diseases due to its functions: downstream genes such as glucose metabolism, angiogenesis, erythropoiesis, and cell survival. Its role can be achieved via two downstream EPO and VEGF strongly related to apoptosis and antioxidant processes. Recently, scientists paid more attention to drugs dealing with the HIF-1 pathway. This review focuses on medicines used for ischemia treatment and their potential HIF-1α pathways. Furthermore, we discussed the interaction between HIF-1α and other biological pathways such as oxidative stress; however, a spotlight has been focused on certain potential signalling contributed to the HIF-1α pathway. HIF-1α is an essential regulator of oxygen balance within cells which affects and controls the expression of thousands of genes related to sustaining homeostasis as oxygen levels fluctuate. HIF-1α's role in ischemic stroke strongly depends on the duration and severity of brain damage after onset. HIF-1α remains difficult to investigate, particularly in ischemic stroke, due to alterations in the acute and chronic phases of the disease, as well as discrepancies between the penumbra and ischemic core. This review emphasizes these contrasts and analyzes the future of this intriguing and demanding field.

Tribbles1 is host protective during in vivo mycobacterial infection

Tuberculosis is a major global health problem and is one of the top 10 causes of death worldwide. There is a pressing need for new treatments that circumvent emerging antibiotic resistance. Mycobacterium tuberculosis parasitises macrophages, reprogramming them to establish a niche in which to proliferate, therefore macrophage manipulation is a potential host-directed therapy if druggable molecular targets could be identified. The pseudokinase Tribbles1 (Trib1) regulates multiple innate immune processes and inflammatory profiles making it a potential drug target in infections. Trib1 controls macrophage function, cytokine production, and macrophage polarisation. Despite wide-ranging effects on leukocyte biology, data exploring the roles of Tribbles in infection in vivo are limited. Here, we identify that human Tribbles1 is expressed in monocytes and is upregulated at the transcript level after stimulation with mycobacterial antigen. To investigate the mechanistic roles of Tribbles in the host response to mycobacteria in vivo, we used a zebrafish Mycobacterium marinum (Mm) infection tuberculosis model. Zebrafish Tribbles family members were characterised and shown to have substantial mRNA and protein sequence homology to their human orthologues. trib1 overexpression was host-protective against Mm infection, reducing burden by approximately 50%. Conversely, trib1 knockdown/knockout exhibited increased infection. Mechanistically, trib1 overexpression significantly increased the levels of proinflammatory factors il-1β and nitric oxide. The host-protective effect of trib1 was found to be dependent on the E3 ubiquitin kinase Cop1. These findings highlight the importance of Trib1 and Cop1 as immune regulators during infection in vivo and suggest that enhancing macrophage TRIB1 levels may provide a tractable therapeutic intervention to improve bacterial infection outcomes in tuberculosis.

Roles of HIF-1α signaling in Mycobacterium tuberculosis infection: New targets for anti-TB therapeutics?

Tuberculosis (TB), a deadly infectious disease induced by Mycobacterium tuberculosis (Mtb), continues to be a global public health issue that kill millions of patents every year. Despite significant efforts have been paid to identify effective TB treatments, the emergence of drug-resistant strains of the disease and the presence of comorbidities in TB patients urges us to explore the detailed mechanisms involved in TB immunity and develop more effective innovative anti-TB strategies. HIF-1α, a protein involved in regulating cellular immune responses during TB infection, has been highlighted as a promising target for the development of novel strategies for TB treatment due to its critical roles in anti-TB host immunity. This review provides a summary of current research progress on the roles of HIF-1α in TB infection, highlighting its importance in regulating the host immune response upon Mtb infection and summarizing the influences and mechanisms of HIF-1α on anti-TB immunological responses of host cells. This review also discusses the various challenges associated with developing HIF-1α as a target for anti-TB therapies, including ensuring specificity and avoiding off-target effects on normal cell function, determining the regulation and expression of HIF-1α in TB patients, and developing drugs that can inhibit HIF-1α. More deep understanding of the molecular mechanisms involved in HIF-1α signaling, its impact on TB host status, and systematic animal testing and clinical trials may benefit the optimization of HIF-1α as a novel therapeutic target for TB.

What can we learn about fish neutrophil and macrophage response to immune challenge from studies in zebrafish

Fish rely, to a high degree, on the innate immune system to protect them against the constant exposure to potential pathogenic invasion from the surrounding water during homeostasis and injury. Zebrafish larvae have emerged as an outstanding model organism for immunity. The cellular component of zebrafish innate immunity is similar to the mammalian innate immune system and has a high degree of sophistication due to the needs of living in an aquatic environment from early embryonic stages of life. Innate immune cells (leukocytes), including neutrophils and macrophages, have major roles in protecting zebrafish against pathogens, as well as being essential for proper wound healing and regeneration. Zebrafish larvae are visually transparent, with unprecedented in vivo microscopy opportunities that, in combination with transgenic immune reporter lines, have permitted visualisation of the functions of these cells when zebrafish are exposed to bacterial, viral and parasitic infections, as well as during injury and healing. Recent findings indicate that leukocytes are even more complex than previously anticipated and are essential for inflammation, infection control, and subsequent wound healing and regeneration.

The Perspective of Using Flow Cytometry for Unpuzzling Hypoxia-Inducible Factors Signalling

Hypoxia-inducible factors (HIFs) are transcription factors that are responsible for adapting to the changes in oxygen levels in the cellular environment. HIF activity determines the expression of cellular proteins that control the development and physiology of the cells and pathophysiology of a disease. Understanding the role of specific HIF (HIF-1-3) in cellular function is essential for development of the HIF-targeted therapies. In this review, we have discussed the use of flow cytometry in analysing HIF function in cells. Proper understanding of HIF-signalling will help to design pharmacological interventions HIF-mediated therapy. We have discussed the role of HIF-signalling in various diseases such as cancer, renal and liver diseases, ulcerative colitis, arthritis, diabetes and diabetic complications, psoriasis, and wound healing. We have also discussed protocols that help to decipher the role of HIFs in these diseases that would eventually help to design promising therapies.

Phenotypic characteristics and immune response of Procypris merus following challenge with aquatic isolate of Klebsiella pneumoniae

Currently, aquaculture is a relatively mature industry; however, disease problems are continuously threatening the industry and hindering its development to a certain extent. Klebsiella pneumoniae is one of the zoonotic bacteria widely present in different hosts and has caused some degree of harm to the aquaculture industry, posing a potential threat to the water environment and indirectly also affecting human food safety issues. In this study, K. pneumoniae was isolated from the aquaculture environment, named as ELD, and subjected to pathogenic and immunological related studies. The results of the study showed that the strain carries at least four virulence-related genes, magA, wabG, ureA and uge, and has developed resistance to at least seven antibacterial drugs, such as amoxicillin, doxycycline, rifampicin, and so on. Moreover, the strain is highly pathogenic and is capable of causing systemic clinical foci in Procypris merus. In addition, after infection with K. pneumoniae, the expression of IL-1β, IL-8, HSP70 and C2 was upregulated in P. merus as a whole, whereas the expression of TNF-α did not change significantly in any of the tissues, which might be a kind of immune response of P. merus against K. pneumoniae infection. This study provides an important theoretical basis for the in-depth exploration of the pathogenic mechanism of K. pneumoniae in fish and the immune response that occurs after the disease is contracted in fish, as well as theoretical support for the development of effective preventive and therapeutic strategies against K. pneumoniae-infected aquatic animals in the future.

Role of HIF in fish inflammation

The hypoxia-inducing factor (HIF) is a central transcription factor in cellular oxygen sensing and regulation. It is common that the inflammation always appears in many diseases, like infectious diseases in fishes, and the inflammation is often accompanied by hypoxia, as a hallmark of inflammation. Besides coordinating cellular responses to low oxygen, HIF-mediated hypoxia signaling pathway is also crucial for immune responses such as the regulations of innate immune cell phenotype and function, as well as metabolic reprogramming under the inflammation. However, the understanding of the molecular mechanisms by which HIFs regulate the inflammatory response in fish is still very limited. Here, we review the characteristics of HIF as well as its roles in innate immune cells and the infections caused by bacteria and viruses. The regulatory effects of HIF on the metabolic reprogramming of innate immune cells are also discussed and the future research directions are outlooked. This paper will serve as a reference for elucidating the molecular mechanism of HIF regulating inflammation and identifying treatment strategies to target HIF for fish disease.

Ex Vivo Production of IL-1β and IL-10 by Activated Blood Cells of Wistar Rats with Different Resistance to Hypoxia after Systemic Inflammatory Response Syndrome

We studied spontaneous and ex vivo activated cytokine production by blood cells of male Wistar rats with different resistance to hypoxia against the background of an LPS-induced systemic inflammatory response. In rats with low (LR) and high resistance (HR) to hypoxia, the number of leukocytes, granulocytes, and peripheral blood lymphocytes was determined, the levels of spontaneous and stimulated production of IL-1β and IL-10 and their ratio were assessed ex vivo. Against the background of a systemic inflammatory response, only HR animals showed a decrease in spontaneous and stimulated production of IL-1β and spontaneous production of IL-10. The IL-1β/IL-10 ratio decreased only in LR rats during the development of a systemic inflammatory response, while in HR animals, no changes in this indicator were observed. The obtained data suggest a high proinflammatory potential of blood cells in LR rats, which apparently determines the development of a more severe course of the systemic inflammatory response.

Neutrophil extracellular traps boost laser-induced mouse choroidal neovascularization through the activation of the choroidal endothelial cell TLR4/HIF-1α pathway

Choroidal neovascularization (CNV) is characterized by the infiltration of immune cells, particularly neutrophils. Neutrophil extracellular trap (NET) facilitates the angiogenesis of pulmonary endothelial cells via activating Toll-like receptor 4 (TLR4). TLR4 promotes the expression of transcription factor hypoxia inducible factor-1α (HIF-1α), which promotes inflammation and angiogenesis via the up-regulation of metalloproteinase-9 (MMP-9) and interleukin-1β (IL-1β). In the present study, we aimed to identify the formation of NET and its role in CNV. Our results showed that NET levels were increased in a mouse laser-induced CNV model via oxidative stress, whereas the inhibition of NET alleviated CNV. In vitro, NET activated the TLR4/HIF-1α pathway in human choroidal endothelial cells (HCECs). Additionally, NET increased the transcription and expression of MMP-9 and IL-1β in HCECs via activating the TLR4/HIF-1α pathway. Meanwhile, NET promoted the inflammatory response accompanied by the proliferation, migration and tube formation of HCECs in a MMP-9- and IL-1β-dependent manner. In conclusion, NET was up-regulated in CNV and promoted the formation of CNV via activating the TLR4/HIF-1α pathway in choroidal endothelial cells. Our data uncovered the novel role of NET in promoting the formation of CNV. The underlying mechanism of NET could be targeted to delay the process of CNV.

Seeing is believing: Efficiency evaluation of multifunctional ionic-dependent AIEgens for tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a significant public health threat with high rates of infection and mortality. Rapid and reliable theranostics of TB are essential to control transmission and shorten treatment duration. In this study, we report two cationic aggregation-inducing emission luminogens (AIEgens) named TTVP and TTPy, which have different functional charged moieties, to investigate their potential for simultaneous tracing and photodynamic therapy in TB infection. TTVP and TTPy exhibit intrinsic positive charges, excellent water solubility, and near-infrared (NIR) emission. Based on ionic-function relationships, TTVP, with more positive charges, demonstrates a stronger binding affinity to Mycobacterium marinum (M.m), (a close genetic relative of Mtb), compared to TTPy. Both TTVP and TTPy exhibit high efficiency in generating reactive oxygen species (ROS) when exposed to white light irradiation, enabling effective photodynamic killing of M.m in vitro. Additionally, we achieved long-term, real-time, noninvasive, continuous tracing, and evaluated therapeutic performance in vivo. Notably, TTVP outperformed TTPy in intracellular killing of M.m, suggesting a possible correlation between the labeling and photodynamic killing abilities of AIEgens. These findings provide valuable insights and a design basis for cationic AIEgens in TB research, offering potential advancements in TB theranostics.

The future of CRISPR in Mycobacterium tuberculosis infection

Clustered Regularly Interspaced Short Palindromic repeats (CRISPR)-Cas systems rapidly raised from a bacterial genetic curiosity to the most popular tool for genetic modifications which revolutionized the study of microbial physiology. Due to the highly conserved nature of the CRISPR locus in Mycobacterium tuberculosis, the etiological agent of one of the deadliest infectious diseases globally, initially, little attention was paid to its CRISPR locus, other than as a phylogenetic marker. Recent research shows that M. tuberculosis has a partially functional Type III CRISPR, which provides a defense mechanism against foreign genetic elements mediated by the ancillary RNAse Csm6. With the advent of CRISPR-Cas based gene edition technologies, our possibilities to explore the biology of M. tuberculosis and its interaction with the host immune system are boosted. CRISPR-based diagnostic methods can lower the detection threshold to femtomolar levels, which could contribute to the diagnosis of the still elusive paucibacillary and extrapulmonary tuberculosis cases. In addition, one-pot and point-of-care tests are under development, and future challenges are discussed. We present in this literature review the potential and actual impact of CRISPR-Cas research on human tuberculosis understanding and management. Altogether, the CRISPR-revolution will revitalize the fight against tuberculosis with more research and technological developments.

Drug screening in zebrafish larvae reveals inflammation-related modulators of secondary damage after spinal cord injury in mice

Prolonged inflammation after spinal cord injury is detrimental to recovery. To find pharmacological modulators of the inflammation response, we designed a rapid drug screening paradigm in larval zebrafish followed by testing of hit compounds in a mouse spinal cord injury model. Methods: We used reduced il-1β linked green fluorescent protein (GFP) reporter gene expression as a read-out for reduced inflammation in a screen of 1081 compounds in larval zebrafish. Hit drugs were tested in a moderate contusion model in mice for cytokine regulation, and improved tissue preservation and locomotor recovery. Results: Three compounds robustly reduced il-1β expression in zebrafish. Cimetidine, an over-the-counter H2 receptor antagonist, also reduced the number of pro-inflammatory neutrophils and rescued recovery after injury in a zebrafish mutant with prolonged inflammation. Cimetidine action on il-1β expression levels was abolished by somatic mutation of H2 receptor hrh2b, suggesting specific action. In mice, systemic treatment with Cimetidine led to significantly improved recovery of locomotor behavior as compared to controls, accompanied by decreased neuronal tissue loss and a shift towards a pro-regenerative profile of cytokine gene expression. Conclusion: Our screen revealed H2 receptor signaling as a promising target for future therapeutic interventions in spinal cord injury. This work highlights the usefulness of the zebrafish model for rapid screening of drug libraries to identify therapeutics to treat mammalian spinal cord injury.

Activated PI3K delta syndrome 1 mutations cause neutrophilia in zebrafish larvae

People with activated PI3 kinase delta syndrome 1 (APDS1) suffer from immune deficiency and severe bronchiectasis. APDS1 is caused by dominant activating mutations of the PIK3CD gene that encodes the PI3 kinase delta (PI3Kδ) catalytic subunit. Despite the importance of innate immunity defects in bronchiectasis, there has been limited investigation of neutrophils or macrophages in APDS1 patients or mouse models. Zebrafish embryos provide an ideal system to study neutrophils and macrophages. We used CRISPR-Cas9 and CRISPR-Cpf1, with oligonucleotide-directed homologous repair, to engineer zebrafish equivalents of the two most prevalent human APDS1 disease mutations. These zebrafish pik3cd alleles dominantly caused excessive neutrophilic inflammation in a tail-fin injury model. They also resulted in total body neutrophilia in the absence of any inflammatory stimulus but normal numbers of macrophages. Exposure of zebrafish to the PI3Kδ inhibitor CAL-101 reversed the total body neutrophilia. There was no apparent defect in neutrophil maturation or migration, and tail-fin regeneration was unimpaired. Overall, the finding is of enhanced granulopoeisis, in the absence of notable phenotypic change in neutrophils and macrophages.

Cardiomyocyte infection by Trypanosoma cruzi promotes innate immune response and glycolysis activation

Introduction

Chagas cardiomyopathy, a disease caused by Trypanosoma cruzi (T. cruzi) infection, is a major contributor to heart failure in Latin America. There are significant gaps in our understanding of the mechanism for infection of human cardiomyocytes, the pathways activated during the acute phase of the disease, and the molecular changes that lead to the progression of cardiomyopathy.

Methods

To investigate the effects of T. cruzi on human cardiomyocytes during infection, we infected induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) with the parasite and analyzed cellular, molecular, and metabolic responses at 3 hours, 24 hours, and 48 hours post infection (hpi) using transcriptomics (RNAseq), proteomics (LC-MS), and metabolomics (GC-MS and Seahorse) analyses.

Results

Analyses of multiomic data revealed that cardiomyocyte infection caused a rapid increase in genes and proteins related to activation innate and adaptive immune systems and pathways, including alpha and gamma interferons, HIF-1α signaling, and glycolysis. These responses resemble prototypic responses observed in pathogen-activated immune cells. Infection also caused an activation of glycolysis that was dependent on HIF-1α signaling. Using gene editing and pharmacological inhibitors, we found that T. cruzi uptake was mediated in part by the glucose-facilitated transporter GLUT4 and that the attenuation of glycolysis, HIF-1α activation, or GLUT4 expression decreased T. cruzi infection. In contrast, pre-activation of pro-inflammatory immune responses with LPS resulted in increased infection rates.

Conclusion

These findings suggest that T. cruzi exploits a HIF-1α-dependent, cardiomyocyte-intrinsic stress-response activation of glycolysis to promote intracellular infection and replication. These chronic immuno-metabolic responses by cardiomyocytes promote dysfunction, cell death, and the emergence of cardiomyopathy.

Butyrate-induced IL-22 expression in fish macrophages contributes to bacterial clearance

IL-22 has been characterized as a critical cytokine in maintaining barrier integrity and host immunity. So far, it has been known that IL-22 is mainly produced by lymphoid lineage cells. In the present study, we have thoroughly investigated butyrate-induced production and function of IL-22 in fish macrophages. Our results demonstrated that short-chain fatty acids (SCFAs), major microbiota-derived metabolites, promoted the expression of IL-22 in head kidney macrophages (HKMs) of turbot (Scophthalmus maximus L.). Interestingly, butyrate-mediated intracellular bacterial killing in HKMs diminished when IL-22 expression was interfered. Furthermore, the turbot fed the diet containing sodium butyrate (NaB) exhibited significantly lower mortality after bacterial infection, compared to the fish fed a basal diet. At the meantime, a higher level of IL-22 expression and bactericidal activity was detected in HKMs from the turbot fed NaB-supplemented diet. In addition, NaB treatment promoted the expression of antimicrobial peptides (AMPs) β-defensins in zebrafish (Danio rerio). However, butyrate-induced expression of AMPs was reduced in IL-22 mutant zebrafish compared to wild-type (WT) fish. Meanwhile, NaB treatment was incapable to protect IL-22 mutant fish from bacterial infection as it did in WT zebrafish. Importantly, our results demonstrated that IL-22 expression was remarkably suppressed in macrophage-depleted zebrafish, indicating that macrophage might be a cell source of IL-22 production in vivo. In conclusion, all these findings collectively revealed that SCFAs regulated the production and function of IL-22 in fish macrophages, which facilitated host resistance to bacterial invasion.

Molecular Actors of Inflammation and Their Signaling Pathways: Mechanistic Insights from Zebrafish

Inflammation is a hallmark of the physiological response to aggressions. It is orchestrated by a plethora of molecules that detect the danger, signal intracellularly, and activate immune mechanisms to fight the threat. Understanding these processes at a level that allows to modulate their fate in a pathological context strongly relies on in vivo studies, as these can capture the complexity of the whole process and integrate the intricate interplay between the cellular and molecular actors of inflammation. Over the years, zebrafish has proven to be a well-recognized model to study immune responses linked to human physiopathology. We here provide a systematic review of the molecular effectors of inflammation known in this vertebrate and recapitulate their modes of action, as inferred from sterile or infection-based inflammatory models. We present a comprehensive analysis of their sequence, expression, and tissue distribution and summarize the tools that have been developed to study their function. We further highlight how these tools helped gain insights into the mechanisms of immune cell activation, induction, or resolution of inflammation, by uncovering downstream receptors and signaling pathways. These progresses pave the way for more refined models of inflammation, mimicking human diseases and enabling drug development using zebrafish models.

Comparative Transcriptome Analysis of Head Kidney of Aeromonas hydrophila-infected Hypoxia-tolerant and Normal Large Yellow Croaker

The large yellow croaker (Larimichthys crocea) is one of the most economically important marine fish on the southeast coast of China and much of its yield is usually lost by hypoxia. To address this problem and lay a foundation for culturing a new strain of large yellow croaker with hypoxia tolerance, our research group screened a hypoxia-tolerant population of L. crocea. Surprisingly, we also found that hypoxia-tolerant population exhibited higher survival when infected with pathogens compared to the normal population during the farming operation. In order to understand the mechanism underlying the higher survival rate of the hypoxia-tolerant population and enrich the head kidney immune mechanism of L. crocea infected with pathogens, we compared and analyzed the head kidney transcriptome of the hypoxia-tolerant and normal individuals under Aeromonas hydrophila infection. We obtained 159.68 GB high-quality reads, of which more than 87.61% were successfully localized to the reference genome of L. crocea. KEGG analysis revealed differentially expressed genes in the signaling pathways involving immunity, cell growth and death, transport and catabolism, and metabolism. Among these, the toll-like receptor signaling pathway, Nod-like receptor signaling pathway, cytokine-cytokine receptor interaction, phagosome, apoptosis, and OXPHOS pathways were enriched in both groups after infection compared to before, and were enriched in infected tolerant individuals compared to normal individuals. In addition, we found that the expression of hif1α and its downstream genes were higher in the hypoxia-sensitive group of fish than in the normal group. In conclusion, our results showed some signaling pathways and hub genes, which may participate in A. hydrophila defense in the head kidney of two populations, and may contribute to the higher survival rate in the hypoxia-tolerant population. Overall, these findings increase our understanding of the defense mechanism within the head kidney of L. crocea under A. hydrophila infection, and suggest a preliminary hypothesis for why hypoxia-tolerant individuals may exhibit a higher survival rates after infection. Our study provides scientific evidence for the breeding of a new hypoxia-tolerant strain of L. crocea for aquaculture.

Macrophage Reprogramming with Anti-miR223-Loaded Artificial Protocells Enhances In Vivo Cancer Therapeutic Potential

Several immune cell-expressed miRNAs (miRs) are associated with altered prognostic outcome in cancer patients, suggesting that they may be potential targets for development of cancer therapies. Here, translucent zebrafish (Danio rerio) is utilized to demonstrate that genetic knockout or knockdown of one such miR, microRNA-223 (miR223), globally or specifically in leukocytes, does indeed lead to reduced cancer progression. As a first step toward potential translation to a clinical therapy, a novel strategy is described for reprogramming neutrophils and macrophages utilizing miniature artificial protocells (PCs) to deliver anti-miRs against the anti-inflammatory miR223. Using genetic and live imaging approaches, it is shown that phagocytic uptake of anti-miR223-loaded PCs by leukocytes in zebrafish (and by human macrophages in vitro) effectively prolongs their pro-inflammatory state by blocking the suppression of pro-inflammatory cytokines, which, in turn, drives altered immune cell-cancer cell interactions and ultimately leads to a reduced cancer burden by driving reduced proliferation and increased cell death of tumor cells. This PC cargo delivery strategy for reprogramming leukocytes toward beneficial phenotypes has implications also for treating other systemic or local immune-mediated pathologies.

High Glucose and Carbonyl Stress Impair HIF-1-Regulated Responses and the Control of Mycobacterium tuberculosis in Macrophages

Diabetes mellitus (DM) increases the risk of developing tuberculosis (TB), but the mechanisms behind diabetes-TB comorbidity are still undefined. Here, we studied the role of hypoxia-inducible factor-1 (HIF-1), a main regulator of metabolic and inflammatory responses, in the outcome of Mycobacterium tuberculosis infection of bone marrow-derived macrophages (BMM). We observed that M. tuberculosis infection of BMM increased the expression of HIF-1α and HIF-1-regulated genes. Treatment with the hypoxia mimetic deferoxamine (DFO) further increased levels of HIF-1-regulated immune and metabolic molecules and diminished the intracellular bacterial load in BMM and in the lungs of infected mice. The expression of HIF-1-regulated immunometabolic genes was reduced, and the intracellular M. tuberculosis levels were increased in BMM incubated with high-glucose levels or with methylglyoxal (MGO), a reactive carbonyl compound elevated in DM. In line with the in vitro findings, high M. tuberculosis levels and low HIF-1-regulated transcript levels were found in the lungs from hyperglycemic Lepr^db/db compared with wild-type mice. The increased intracellular M. tuberculosis growth and the reduced expression of HIF-1-regulated metabolic and inflammatory genes in BMM incubated with MGO or high glucose were reverted by additional treatment with DFO. Hif1a-deficient BMM showed ablated responses of immunometabolic transcripts after mycobacterial infection at normal or high-glucose levels. We propose that HIF-1 may be targeted for the control of M. tuberculosis during DM. IMPORTANCE People living with diabetes who are also infected with M. tuberculosis are more likely to develop tuberculosis disease (TB). Why diabetic patients have an increased risk for developing TB is not well understood. Macrophages, the cell niche for M. tuberculosis, can express microbicidal mechanisms or be permissive to mycobacterial persistence and growth. Here, we showed that high glucose and carbonyl stress, which mediate diabetes pathogenesis, impair the control of intracellular M. tuberculosis in macrophages. Infection with M. tuberculosis stimulated the expression of genes regulated by the transcription factor HIF-1, a major controller of the responses to hypoxia, resulting in macrophage activation. High glucose and carbonyl compounds inhibited HIF-1 responses by macrophages. Mycobacterial control in the presence of glucose or carbonyl stress was restored by DFO, a compound that stabilizes HIF-1. We propose that HIF-1 can be targeted to reduce the risk of developing TB in people with diabetes.

A Fun-Guide to Innate Immune Responses to Fungal Infections

Immunocompromised individuals are at high risk of developing severe fungal infections with high mortality rates, while fungal pathogens pose little risk to most healthy people. Poor therapeutic outcomes and growing antifungal resistance pose further challenges for treatments. Identifying specific immunomodulatory mechanisms exploited by fungal pathogens is critical for our understanding of fungal diseases and development of new therapies. A gap currently exists between the large body of literature concerning the innate immune response to fungal infections and the potential manipulation of host immune responses to aid clearance of infection. This review considers the innate immune mechanisms the host deploys to prevent fungal infection and how these mechanisms fail in immunocompromised hosts. Three clinically relevant fungal pathogens (Candida albicans, Cryptococcus spp. and Aspergillus spp.) will be explored. This review will also examine potential mechanisms of targeting the host therapeutically to improve outcomes of fungal infection.

TLR22-Induced Pro-Apoptotic mtROS Abets UPRmt-Mediated Mitochondrial Fission in Aeromonas hydrophila-Infected Headkidney Macrophages of Clarias gariepinus

Toll-like receptors (TLRs) are epitomized as the first line of defense against pathogens. Amongst TLRs, TLR22 is expressed in non-mammalian aquatic vertebrates, including fish. Using headkidney macrophages (HKM) of Clarias gariepinus, we reported the pro-apoptotic and microbicidal role of TLR22 in Aeromonas hydrophila infection. Mitochondria act as a central scaffold in the innate immune system. However, the precise molecular mechanisms underlying TLR22 signaling and mitochondrial involvement in A. hydrophila-pathogenesis remain unexplored in fish. The aim of the present study was to investigate the nexus between TLR22 and mitochondria in pro-apoptotic immune signaling circuitry in A. hydrophila-infected HKM. We report that TLR22-induced mitochondrial-Ca²⁺ [Ca²⁺]_mt surge is imperative for mtROS production in A. hydrophila-infected HKM. Mitigating mtROS production enhanced intracellular bacterial replication implicating its anti-microbial role in A. hydrophila-pathogenesis. Enhanced mtROS triggers hif1a expression leading to prolonged chop expression. CHOP prompts mitochondrial unfolded protein response (UPR^mt) leading to the enhanced expression of mitochondrial fission marker dnml1, implicating mitochondrial fission in A. hydrophila pathogenesis. Inhibition of mitochondrial fission reduced HKM apoptosis and increased the bacterial burden. Additionally, TLR22-mediated alterations in mitochondrial architecture impair mitochondrial function (ΔΨ_m loss and cytosolic accumulation of cyt c), which in turn activates caspase-9/caspase-3 axis in A. hydrophila-infected HKM. Based on these findings we conclude that TLR22 prompts mtROS generation, which activates the HIF-1α/CHOP signalosome triggering UPR^mt-induced mitochondrial fragmentation culminating in caspase-9/-3-mediated HKM apoptosis and bacterial clearance.

The effect of HIF on metabolism and immunity

Cellular hypoxia occurs when the demand for sufficient molecular oxygen needed to produce the levels of ATP required to perform physiological functions exceeds the vascular supply, thereby leading to a state of oxygen depletion with the associated risk of bioenergetic crisis. To protect against the threat of hypoxia, eukaryotic cells have evolved the capacity to elicit oxygen-sensitive adaptive transcriptional responses driven primarily (although not exclusively) by the hypoxia-inducible factor (HIF) pathway. In addition to the canonical regulation of HIF by oxygen-dependent hydroxylases, multiple other input signals, including gasotransmitters, non-coding RNAs, histone modifiers and post-translational modifications, modulate the nature of the HIF response in discreet cell types and contexts. Activation of HIF induces various effector pathways that mitigate the effects of hypoxia, including metabolic reprogramming and the production of erythropoietin. Drugs that target the HIF pathway to induce erythropoietin production are now approved for the treatment of chronic kidney disease-related anaemia. However, HIF-dependent changes in cell metabolism also have profound implications for functional responses in innate and adaptive immune cells, and thereby heavily influence immunity and the inflammatory response. Preclinical studies indicate a potential use of HIF therapeutics to treat inflammatory diseases, such as inflammatory bowel disease. Understanding the links between HIF, cellular metabolism and immunity is key to unlocking the full therapeutic potential of drugs that target the HIF pathway.

Hypoxia-dependent changes in cellular metabolism have important implications for the effective functioning of multiple immune cell subtypes. This Review describes the inputs that shape the hypoxic response in individual cell types and contexts, and the implications of this response for cellular metabolism and associated alterations in immune cell function.

Hypoxia is a common feature of particular microenvironments and at sites of immunity and inflammation, resulting in increased activity of the hypoxia-inducible factor (HIF).

In addition to hypoxia, multiple inputs modulate the activity of the HIF pathway, allowing nuanced downstream responses in discreet cell types and contexts.

HIF-dependent changes in cellular metabolism mitigate the effects of hypoxia and ensure that energy needs are met under conditions in which oxidative phosphorylation is reduced.

HIF-dependent changes in metabolism also profoundly affect the phenotype and function of immune cells.

The immunometabolic effects of HIF have important implications for targeting the HIF pathway in inflammatory disease.

Hypoxia regulates cytokines expression and neutrophils migration by ERK signaling in zebrafish

Normal dissolved oxygen in water is essential for maintaining the physiological functions of fish, but environmental pollution, such as eutrophication can lead to a decrease in oxygen content in water. How this reduction of dissolved oxygen in water affects the immune functions of fish and the potential regulatory mechanisms have not been thoroughly elucidated. In this study, we made full use of the aquatic model animal zebrafish to explore this question. In a model of LPS-induced inflammation, we found that hypoxia induced by infusing nitrogen into water increased the expression of pro-inflammatory cytokines, such as il-1β, il-6, and il-8. In vivo imaging also showed that hypoxia significantly increased neutrophil migration to the site of caudal fin injury in the transgenic line. Subsequently, we found that the phosphorylation level of ERK protein was significantly activated upon hypoxia and proved the roles of ERK signaling in the expression of pro-inflammatory cytokines and neutrophil migration in zebrafish. This study indicated that reduced water oxygen significantly increases the inflammatory response of the zebrafish.

Inflammatory response in hematopoietic stem and progenitor cells triggered by activating SHP2 mutations evokes blood defects

Gain-of-function mutations in the protein-tyrosine phosphatase SHP2 are the most frequently occurring mutations in sporadic juvenile myelomonocytic leukemia (JMML) and JMML-like myeloproliferative neoplasm (MPN) associated with Noonan syndrome (NS). Hematopoietic stem and progenitor cells (HSPCs) are the disease propagating cells of JMML. Here, we explored transcriptomes of HSPCs with SHP2 mutations derived from JMML patients and a novel NS zebrafish model. In addition to major NS traits, CRISPR/Cas9 knock-in Shp2D61G mutant zebrafish recapitulated a JMML-like MPN phenotype, including myeloid lineage hyperproliferation, ex vivo growth of myeloid colonies, and in vivo transplantability of HSPCs. Single-cell mRNA sequencing of HSPCs from Shp2D61G zebrafish embryos and bulk sequencing of HSPCs from JMML patients revealed an overlapping inflammatory gene expression pattern. Strikingly, an anti-inflammatory agent rescued JMML-like MPN in Shp2D61G zebrafish embryos. Our results indicate that a common inflammatory response was triggered in the HSPCs from sporadic JMML patients and syndromic NS zebrafish, which potentiated MPN and may represent a future target for JMML therapies.

Fluorescence-Activated Cell Sorting and Quantitative Real-Time PCR to Reveal VEGF-Expressing Macrophage Populations in the Zebrafish Larvae

The transparent, genetically tractable zebrafish is increasingly recognized as a useful model to both live image and uncover mechanistic insight into cell interactions governing tissue homeostasis, pathology, and regeneration. Here, we describe a protocol for the isolation of macrophages from zebrafish wounds using fluorescence-activated cell sorting (FACS), and the identification of specific pro-angiogenic macrophage populations that express high levels of vascular endothelial growth factor (vegf) using quantitative real-time PCR (qPCR). The cell dissociation and FACS sorting techniques have been optimized for immune cells and successfully used to isolate other fluorescently marked populations within the wound such as neutrophils and endothelial cells. More broadly, this protocol can be easily adapted to other contexts where identification of pro-angiogenic immune cells is transformative for understanding, from development to pathologies such as infection, cancer, and diabetes.

Infection by High-Risk Human Papillomaviruses, Epithelial-to-Mesenchymal Transition and Squamous Pre-Malignant or Malignant Lesions of the Uterine Cervix: A Series of Chained Events?

Wound healing requires static epithelial cells to gradually assume a mobile phenotype through a multi-step process termed epithelial-to-mesenchymal transition (EMT). Although it is inherently transient and reversible, EMT perdures and is abnormally activated when the epithelium is chronically exposed to pathogens: this event deeply alters the tissue and eventually contributes to the development of diseases. Among the many of them is uterine cervical squamous cell carcinoma (SCC), the most frequent malignancy of the female genital system. SCC, whose onset is associated with the persistent infection of the uterine cervix by high-risk human papillomaviruses (HR-HPVs), often relapses and/or metastasizes, being resistant to conventional chemo- or radiotherapy. Given that these fearsome clinical features may stem, at least in part, from the exacerbated and long-lasting EMT occurring in the HPV-infected cervix; here we have reviewed published studies concerning the impact that HPV oncoproteins, cellular tumor suppressors, regulators of gene expression, inflammatory cytokines or growth factors, and the interactions among these effectors have on EMT induction and cervical carcinogenesis. It is predictable and desirable that a broader comprehension of the role that EMT inducers play in SCC pathogenesis will provide indications to flourish new strategies directed against this aggressive tumor.

SF5- and SCF3-substituted tetrahydroquinoline compounds as potent bactericidal agents against multidrug-resistant persister Gram-positive bacteria

Bacteria persister cells are immune to most antibiotics and hence compounds that are active against persister bacteria are needed. We screened a chemical library of SF₅- and SCF₃-substituted tetrahydroquinoline compounds, synthesized via the Povarov reaction, for antibacterial activity and identified active compounds that displayed good activities against many Gram-positive bacteria, including persisters. The most potent of these compounds, HSD1835, inhibited the growth of drug-resistant Gram-positive bacterial pathogens (including clinical strains) at concentrations ranging from 1 μg mL^-1 to 4 μg mL^-1. Several of the SCF₃- and SF₅-containing compounds were active against methicillin-resistant Staphylococcus aureus (MRSA) and against the two most fatal strains of vancomycin-resistant Enterococcus (VRE), VRE faecalis and VRE faecium. The compounds showed bactericidal activity against stationary phase persister MRSA in time-kill assays. Mechanistic studies showed that HSD1835 acts by disrupting bacterial membranes. Scanning electron microscopy (SEM) was used to confirm bacterial membrane disruption. Interestingly, in a 30 day serial exposure experiment, MRSA remained susceptible to low-dose HSD1835 whilst resistance to ciprofloxacin and mupirocin emerged by day 10. Analogs of HSD1835, which did not bear the SF₅ or SCF₃ moieties, were inactive against bacteria. Recent reports (G. A. Naclerio, N. S. Abutaleb, K. I. Onyedibe, M. N. Seleem and H. O. Sintim, RSC Med. Chem. 2020, 11, 102-110 and G. A. Naclerio, N. S. Abutaleb, D. Li, M. N. Seleem and H. O. Sintim, J. Med. Chem. 2020, 63(20), 11934-11944) also demonstrated that adding the SF₅ or SCF₃ groups to a different scaffold (oxadiazoles) enhanced the antibacterial properties of the compounds, so it appears that these groups are privileged moieties that enhance the antimicrobial activities of compounds.

Climate change affects the parasitism rate and impairs the regulation of genes related to oxidative stress and ionoregulation of Colossoma macropomum

Global climate change represents a critical threat to the environment since it influences organismic interactions, such as the host-parasite systems, mainly in ectotherms including fishes. Rising temperature and CO₂ are predicted to affect this interaction other and critical physiological processes in fish. Herein, we investigated the effects of different periods of exposure to climate change scenarios and to two degrees of parasitism by monogeneans in the host-parasite interaction, as well as the antioxidant and ionoregulatory responses of tambaqui (Colossoma macropomum), an important species in South American fishing and aquaculture. We hypothesized that temperature and CO₂ changes in combination with parasite infection would interfere with the host's physiological processes that are related to oxidative stress and ionoregulation. We experimentally exposed C. macropomum to low and high levels of parasitism in the current and extreme climate scenarios (4.5 °C and 900 ppm CO₂ above current levels) for periods of seven and thirty days and we use as analyzed factors; the exposure time, the climate scenario and parasitism level in a 2 × 2 × 2 factorial through a three-way ANOVA as being fish the experimental unit (n = 8). An analysis of gill enzymatic and gene expression profile was performed to assess physiological (SOD, GPx and Na⁺/K⁺-ATPase enzymes) and molecular (Nrf2, SOD1, HIF-1α and NKA α1a genes) responses. A clear difference in the parasitism levels of individuals exposed to the extreme climate scenario was observed with a rapid and aggressive increase that was higher after 7 days of exposure though showed a decrease after 30 days. The combination of exposure to the extreme climate change scenario and parasitism caused oxidative stress and osmoregulatory disturbance, which was observed through the analysis of gene expression (Nrf2, SOD1, HIF-1α and NKA α1a) and antioxidant and ionoregulatory enzymes (SOD, GPx and Na⁺/K⁺-ATPase) on the host, possibly linked to inflammatory processes caused by the high degree of parasitism. In the coming years, these conditions may result in losses of performance for this species, and as such will represent ecological damage and economical losses, and result in a possible vulnerability in relation to food security.

A fresh look at mycobacterial pathogenicity with the zebrafish host model

The zebrafish has earned its place among animal models to study tuberculosis and other infections caused by pathogenic mycobacteria. This model host is especially useful to study the role of granulomas, the inflammatory lesions characteristic of mycobacterial disease. The optically transparent zebrafish larvae provide a window on the initial stages of granuloma development in the context of innate immunity. Application of fluorescent dyes and transgenic markers enabled real-time visualization of how innate immune mechanisms, such as autophagy and inflammasomes, are activated in infected macrophages and how propagating calcium signals drive communication between macrophages during granuloma formation. A combination of imaging, genetic, and chemical approaches has revealed that the interplay between macrophages and mycobacteria is the main driver of tissue dissemination and granuloma development, while neutrophils have a protective function in early granulomas. Different chemokine signaling axes, conserved between humans and zebrafish, have been shown to recruit macrophages permissive to mycobacterial growth, control their microbicidal capacity, drive their spreading and aggregation, and mediate granuloma vascularization. Finally, zebrafish larvae are now exploited to explore cell death processes, emerging as crucial factors in granuloma expansion. In this review, we discuss recent advances in the understanding of mycobacterial pathogenesis contributed by zebrafish models.

A Dietary Cholesterol-Based Intestinal Inflammation Assay for Improving Drug-Discovery on Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) with chronic infiltration of immune cells in the gastrointestinal tract are common and largely incurable. The therapeutic targeting of IBD has been hampered by the complex causality of the disease, with environmental insults like cholesterol-enriched Western diets playing a critical role. To address this drug development challenge, we report an easy-to-handle dietary cholesterol-based in vivo assay that allows the screening of immune-modulatory therapeutics in transgenic zebrafish models. An improvement in the feeding strategy with high cholesterol diet (HCD) selectively induces a robust and consistent infiltration of myeloid cells in larvae intestines that is highly suitable for compound discovery efforts. Using transgenics with fluorescent reporter expression in neutrophils, we take advantage of the unique zebrafish larvae clarity to monitor an acute inflammatory response in a whole organism context with a fully functional innate immune system. The use of semi-automated image acquisition and processing combined with quantitative image analysis allows categorizing anti- or pro-inflammatory compounds based on a leukocytic inflammation index. Our HCD gut inflammation (HCD-GI) assay is simple, cost- and time-effective as well as highly physiological which makes it unique when compared to chemical-based zebrafish models of IBD. Besides, diet is a highly controlled, selective and targeted trigger of intestinal inflammation that avoids extra-intestinal outcomes and reduces the chances of chemical-induced toxicity during screenings. We show the validity of this assay for a screening platform by testing two dietary phenolic acids, namely gallic acid (GA; 3,4,5-trihydroxybenzoic acid) and ferulic acid (FA; 4-hydroxy-3-methoxycinnamic acid), with well described anti-inflammatory actions in animal models of IBD. Analysis of common IBD therapeutics (Prednisolone and Mesalamine) proved the fidelity of our IBD-like intestinal inflammation model. In conclusion, the HCD-GI assay can facilitate and accelerate drug discovery efforts on IBD, by identification of novel lead molecules with immune modulatory action on intestinal neutrophilic inflammation. This will serve as a jumping-off point for more profound analyses of drug mechanisms and pathways involved in early IBD immune responses.

Understanding Metabolic Regulation Between Host and Pathogens: New Opportunities for the Development of Improved Therapeutic Strategies Against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb) causes chronic granulomatous lung disease in humans. Recently, novel strategies such as host-directed therapeutics and adjunctive therapies that enhance the effect of existing antibiotics have emerged to better control Mtb infection. Recent advances in understanding the metabolic interplay between host immune cells and pathogens have provided new insights into how their interactions ultimately influence disease outcomes and antibiotic-treatment efficacy. In this review, we describe how metabolic cascades in immune environments and relevant metabolites produced from immune cells during Mtb infection play critical roles in the progression of diseases and induction of anti-Mtb protective immunity. In addition, we introduce how metabolic alterations in Mtb itself can lead to the development of persister cells that are resistant to host immunity and can eventually evade antibiotic attacks. Further understanding of the metabolic link between host cells and Mtb may contribute to not only the prevention of Mtb persister development but also the optimization of host anti-Mtb immunity together with enhanced efficacy of existing antibiotics. Overall, this review highlights novel approaches to improve and develop host-mediated therapeutic strategies against Mtb infection by restoring and switching pathogen-favoring metabolic conditions with host-favoring conditions.

Genetic Approaches Using Zebrafish to Study the Microbiota-Gut-Brain Axis in Neurological Disorders

The microbiota-gut-brain axis (MGBA) is a bidirectional signaling pathway mediating the interaction of the microbiota, the intestine, and the central nervous system. While the MGBA plays a pivotal role in normal development and physiology of the nervous and gastrointestinal system of the host, its dysfunction has been strongly implicated in neurological disorders, where intestinal dysbiosis and derived metabolites cause barrier permeability defects and elicit local inflammation of the gastrointestinal tract, concomitant with increased pro-inflammatory cytokines, mobilization and infiltration of immune cells into the brain, and the dysregulated activation of the vagus nerve, culminating in neuroinflammation and neuronal dysfunction of the brain and behavioral abnormalities. In this topical review, we summarize recent findings in human and animal models regarding the roles of the MGBA in physiological and neuropathological conditions, and discuss the molecular, genetic, and neurobehavioral characteristics of zebrafish as an animal model to study the MGBA. The exploitation of zebrafish as an amenable genetic model combined with in vivo imaging capabilities and gnotobiotic approaches at the whole organism level may reveal novel mechanistic insights into microbiota-gut-brain interactions, especially in the context of neurological disorders such as autism spectrum disorder and Alzheimer's disease.

Lactate Metabolism and Signaling in Tuberculosis and Cancer: A Comparative Review

Infection with Mycobacterium tuberculosis (Mtb) leading to tuberculosis (TB) disease continues to be a major global health challenge. Critical barriers, including but not limited to the development of multi-drug resistance, lack of diagnostic assays that detect patients with latent TB, an effective vaccine that prevents Mtb infection, and infectious and non-infectious comorbidities that complicate active TB, continue to hinder progress toward a TB cure. To complement the ongoing development of new antimicrobial drugs, investigators in the field are exploring the value of host-directed therapies (HDTs). This therapeutic strategy targets the host, rather than Mtb, and is intended to augment host responses to infection such that the host is better equipped to prevent or clear infection and resolve chronic inflammation. Metabolic pathways of immune cells have been identified as promising HDT targets as more metabolites and metabolic pathways have shown to play a role in TB pathogenesis and disease progression. Specifically, this review highlights the potential role of lactate as both an immunomodulatory metabolite and a potentially important signaling molecule during the host response to Mtb infection. While long thought to be an inert end product of primarily glucose metabolism, the cancer research field has discovered the importance of lactate in carcinogenesis and resistance to chemotherapeutic drug treatment. Herein, we discuss similarities between the TB granuloma and tumor microenvironments in the context of lactate metabolism and identify key metabolic and signaling pathways that have been shown to play a role in tumor progression but have yet to be explored within the context of TB. Ultimately, lactate metabolism and signaling could be viable HDT targets for TB; however, critical additional research is needed to better understand the role of lactate at the host-pathogen interface during Mtb infection before adopting this HDT strategy.

Hypoxia-inducible factor-1α involved in macrophage regulation in ayu (Plecoglossus altivelis) under hypoxia

Hypoxia-inducible factor-1α (HIF-1α) plays a critical role in immune and inflammatory responses and is important in controlling a variety of processes in monocytes and macrophages. However, the role of HIF-1α in the teleost immune system remains less known. In this study, we cloned the cDNA sequence of HIF-1α from the ayu (Plecoglossus altivelis, PaHIF-1α). Sequence and phylogenetic tree analysis showed that PaHIF-1α clustered within the fish HIF-1α tree and was closely related to that of Northern pike (Esox lucius). PaHIF-1α was expressed in all tested tissues and expression increased in liver, head kidney, and body kidney upon Vibrio anguillarum infection. PaHIF-1α was found to regulate the expression of cytokines in ayu monocytes/macrophages (MO/MФ). PaHIF-1α mediated hypoxia-induced enhancement of MO/MФ phagocytic and bactericidal activities to enhance host defenses. Compared with the control, intermittent hypoxia further increased the expression of PaHIF-1α mRNA, improved the survival rate, and reduced the bacterial load of V. anguillarum-infected ayu. Therefore, PaHIF-1α may play a predominant role in the modulation of ayu MO/MФ function.

The New Frontier of Host-Directed Therapies for Mycobacterium avium Complex

Mycobacterium avium complex (MAC) is an increasingly important cause of morbidity and mortality, and is responsible for pulmonary infection in patients with underlying lung disease and disseminated disease in patients with AIDS. MAC has evolved various virulence strategies to subvert immune responses and persist in the infected host. Current treatment for MAC is challenging, requiring a combination of multiple antibiotics given over a long time period (for at least 12 months after negative sputum culture conversion). Moreover, even after eradication of infection, many patients are left with residual lung dysfunction. In order to address similar challenges facing the management of patients with tuberculosis, recent attention has focused on the development of novel adjunctive, host-directed therapies (HDTs), with the goal of accelerating the clearance of mycobacteria by immune defenses and reducing or reversing mycobacterial-induced lung damage. In this review, we will summarize the evidence supporting specific adjunctive, HDTs for MAC, with a focus on the repurposing of existing immune-modulatory agents targeting a variety of different cellular pathways. We also highlight areas meriting further investigation.

Blood in the water: recent uses of zebrafish to study myeloid biology

PURPOSE OF REVIEW

Myeloid cells contribute to immune response to infection and tissue regeneration after injury as well as to the developmental induction of the hematopoietic system overall. Here we review recent uses of zebrafish to advance the study of myeloid biology in development and disease.

RECENT FINDINGS

Recent studies have made use of advanced imaging and genetic strategies and have highlighted key concepts in myeloid cell behavior. These include immune-cell cross-talk and subpopulation response in infection and regeneration, and tightly regulated inflammatory and tissue remodeling behaviors in development.

SUMMARY

These new findings will shape our understanding of the developmental origins of immune populations as well as their specific cellular behaviors at all stages of infection, regeneration, and myeloid neoplasms.

Loss of the tumor suppressor BTG3 drives a pro-angiogenic tumor microenvironment through HIF-1 activation

B-cell translocation gene 3 (BTG3) is a member of the antiproliferative BTG gene family and is a downstream target of p53. Here, we show that senescence triggered by BTG3 depletion was accompanied by a secretome enriched with cytokines, growth factors, and matrix-remodeling enzymes, which could promote angiogenesis and cell scattering in vitro. We present evidence that at least part of these activities can be explained by elevated HIF-1α activity. Mechanistically, the BTG3 C-terminal domain competes with the coactivator p300 for binding the HIF-1α transactivation domain. The angiogenic promoting effect of BTG3 knockdown was largely diminished upon co-depletion of HIF-1α, indicating that HIF-1α is a major downstream target of BTG3 in the control of angiogenesis. In vivo, ectopic expression of BTG3 suppresses angiogenesis in xenograft tumors; and syngenic tumor growth and metastasis were enhanced in Btg3-null mice. Moreover, analysis of clinical datasets revealed that a higher BTG3/VEGFA expression ratio correlates with improved patient survival in a number of cancer types. Taken together, our findings highlight the non-autonomous regulation of tumor microenvironment by BTG3 while suppressing tumor progression.

Zebrafish cardiac regeneration-looking beyond cardiomyocytes to a complex microenvironment

The study of heart repair post-myocardial infarction has historically focused on the importance of cardiomyocyte proliferation as the major factor limiting adult mammalian heart regeneration. However, there is mounting evidence that a narrow focus on this one cell type discounts the importance of a complex cascade of cell-cell communication involving a whole host of different cell types. A major difficulty in the study of heart regeneration is the rarity of this process in adult animals, meaning a mammalian template for how this can be achieved is lacking. Here, we review the adult zebrafish as an ideal and unique model in which to study the underlying mechanisms and cell types required to attain complete heart regeneration following cardiac injury. We provide an introduction to the role of the cardiac microenvironment in the complex regenerative process and discuss some of the key advances using this in vivo vertebrate model that have recently increased our understanding of the vital roles of multiple different cell types. Due to the sheer number of exciting studies describing new and unexpected roles for inflammatory cell populations in cardiac regeneration, this review will pay particular attention to these important microenvironment participants.

Mechanisms controlling bacterial infection in myeloid cells under hypoxic conditions

Various factors of the tissue microenvironment such as the oxygen concentration influence the host-pathogen interaction. During the past decade, hypoxia-driven signaling via hypoxia-inducible factors (HIF) has emerged as an important factor that affects both the pathogen and the host. In this chapter, we will review the current knowledge of this complex interplay, with a particular emphasis given to the impact of hypoxia and HIF on the inflammatory and antimicrobial activity of myeloid cells, the bacterial responses to hypoxia and the containment of bacterial infections under oxygen-limited conditions. We will also summarize how low oxygen concentrations influence the metabolism of neutrophils, macrophages and dendritic cells. Finally, we will discuss the consequences of hypoxia and HIFα activation for the invading pathogen, with a focus on Pseudomonas aeruginosa, Mycobacterium tuberculosis, Coxiella burnetii, Salmonella enterica and Staphylococcus aureus. This includes a description of the mechanisms and microbial factors, which the pathogens use to sense and react to hypoxic conditions.

Metabolic Regulation of Inflammasome Activity Controls Embryonic Hematopoietic Stem and Progenitor Cell Production

Embryonic hematopoietic stem and progenitor cells (HSPCs) robustly proliferate while maintaining multilineage potential in vivo; however, an incomplete understanding of spatiotemporal cues governing their generation has impeded robust production from human induced pluripotent stem cells (iPSCs) in vitro. Using the zebrafish model, we demonstrate that NLRP3 inflammasome-mediated interleukin-1-beta (IL1β) signaling drives HSPC production in response to metabolic activity. Genetic induction of active IL1β or pharmacologic inflammasome stimulation increased HSPC number as assessed by in situ hybridization for runx1/cmyb and flow cytometry. Loss of inflammasome components, including il1b, reduced CD41⁺ HSPCs and prevented their expansion in response to metabolic cues. Cell ablation studies indicated that macrophages were essential for initial inflammasome stimulation of Il1rl1⁺ HSPCs. Significantly, in human iPSC-derived hemogenic precursors, transient inflammasome stimulation increased multilineage hematopoietic colony-forming units and T cell progenitors. This work establishes the inflammasome as a conserved metabolic sensor that expands HSPC production in vivo and in vitro.

Effect of sodium (S)-2-hydroxyglutarate in male, and succinic acid in female Wistar rats against renal ischemia-reperfusion injury, suggesting a role of the HIF-1 pathway

Background

Ischemia–reperfusion (IR) injury is the main cause of delayed graft function in solid organ transplantation. Hypoxia-inducible factors (HIFs) control the expression of genes related to preconditioning against IR injury. During normoxia, HIF-α subunits are marked for degradation by the egg-laying defective nine homolog (EGLN) family of prolyl-4-hydroxylases. The inhibition of EGLN stabilizes HIFs and protects against IR injury. The aim of this study was to determine whether the EGLN inhibitors sodium (S)-2-hydroxyglutarate [(S)-2HG] and succinic acid (SA) have a nephroprotective effect against renal IR injury in Wistar rats.

Methods

(S)-2HG was synthesized in a 22.96% yield from commercially available L-glutamic acid in a two-step methodology (diazotization/alkaline hydrolysis), and its structure was confirmed by nuclear magnetic resonance and polarimetry. SA was acquired commercially. (S)-2HG and SA were independently evaluated in male and female Wistar rats respectively after renal IR injury. Rats were divided into the following groups: sham (SH), nontoxicity [(S)-2HG: 12.5 or 25 mg/kg; SA: 12.5, 25, or 50 mg/kg], IR, and compound+IR [(S)-2HG: 12.5 or 25 mg/kg; SA: 12.5, 25, or 50 mg/kg]; independent SH and IR groups were used for each assessed compound. Markers of kidney injury (BUN, creatinine, glucose, and uric acid) and liver function (ALT, AST, ALP, LDH, serum proteins, and albumin), proinflammatory cytokines (IL-1β, IL-6, and TNF-α), oxidative stress biomarkers (malondialdehyde and superoxide dismutase), and histological parameters (tubular necrosis, acidophilic casts, and vascular congestion) were assessed. Tissue HIF-1α was measured by ELISA and Western blot, and the expression of Hmox1 was assessed by RT-qPCR.

Results

(S)-2HG had a dose-dependent nephroprotective effect, as evidenced by a significant reduction in the changes in the BUN, creatinine, ALP, AST, and LDH levels compared with the IR group. Tissue HIF-1α was only increased in the IR group compared to SH; however, (S)-2HG caused a significant increase in the expression of Hmox1, suggesting an early accumulation of HIF-1α in the (S)-2HG-treated groups. There were no significant effects on the other biomarkers. SA did not show a nephroprotective effect; the only changes were a decrease in creatinine level at 12.5 mg/kg and increased IR injury at 50 mg/kg. There were no effects on the other biochemical, proinflammatory, or oxidative stress biomarkers.

Conclusion

None of the compounds were hepatotoxic at the tested doses. (S)-2HG showed a dose-dependent nephroprotective effect at the evaluated doses, which involved an increase in the expression of Hmox1, suggesting stabilization of HIF-1α. SA did not show a nephroprotective effect but tended to increase IR injury when given at high doses.

Zebrafish as a Model for Fish Diseases in Aquaculture

The use of zebrafish as a model for human conditions is widely recognized. Within the last couple of decades, the zebrafish has furthermore increasingly been utilized as a model for diseases in aquacultured fish species. The unique tools available in zebrafish present advantages compared to other animal models and unprecedented in vivo imaging and the use of transgenic zebrafish lines have contributed with novel knowledge to this field. In this review, investigations conducted in zebrafish on economically important diseases in aquacultured fish species are included. Studies are summarized on bacterial, viral and parasitic diseases and described in relation to prophylactic approaches, immunology and infection biology. Considerable attention has been assigned to innate and adaptive immunological responses. Finally, advantages and drawbacks of using the zebrafish as a model for aquacultured fish species are discussed.

If it's not one thing, HIF's another: immunoregulation by hypoxia inducible factors in disease

Hypoxia‐inducible factors (HIFs) have emerged in recent years as critical regulators of immunity. Localised, low oxygen tension is a hallmark of inflamed and infected tissues. Subsequent myeloid cell HIF stabilisation plays key roles in the innate immune response, alongside emerging oxygen‐independent roles. Manipulation of regulatory proteins of the HIF transcription factor family can profoundly influence inflammatory profiles, innate immune cell function and pathogen clearance and, as such, has been proposed as a therapeutic strategy against inflammatory diseases. The direction and mode of HIF manipulation as a therapy are dictated by the inflammatory properties of the disease in question, with innate immune cell HIF reduction being, in general, advantageous during chronic inflammatory conditions, while upregulation of HIF is beneficial during infections. The therapeutic potential of targeting myeloid HIFs, both genetically and pharmacologically, has been recently illuminated in vitro and in vivo, with an emerging range of inhibitory and activating strategies becoming available. This review focuses on cutting edge findings that uncover the roles of myeloid cell HIF signalling on immunoregulation in the contexts of inflammation and infection and explores future directions of potential therapeutic strategies.

A zebrafish model of tuberculosis comorbidity and the effects of HIF-activating intervention

Comorbidities are an important factor in tuberculosis pathophysiology and treatment but are understudied in animal models. Schild et al. present a zebrafish model of Mycobacterium marinum infection and wound comorbidity that retains responsiveness to protective hypoxia-inducible factor-1α activation as an example of a host-directed therapy. This platform is a new paradigm for the zebrafish-M. marinum infection model and provides a blueprint to test therapeutic interventions on infection and comorbid pathologies. Comment on: https://doi.org/10.1111/febs.15433.

Hif-1alpha stabilisation is protective against infection in zebrafish comorbid models

Multi-drug-resistant tuberculosis is a worldwide problem, and there is an urgent need for host-derived therapeutic targets, circumventing emerging drug resistance. We have previously shown that hypoxia-inducible factor-1α (Hif-1α) stabilisation helps the host to clear mycobacterial infection via neutrophil activation. However, Hif-1α stabilisation has also been implicated in chronic inflammatory diseases caused by prolonged neutrophilic inflammation. Comorbid infection and inflammation can be found together in disease settings, and it remains unclear whether Hif-1α stabilisation would be beneficial in a holistic disease setting. Here, we set out to understand the effects of Hif-1α on neutrophil behaviour in a comorbid setting by combining two well-characterised in vivo zebrafish models - TB infection (Mycobacterium marinum infection) and sterile injury (tailfin transection). Using a local Mm infection near to the tailfin wound site caused neutrophil migration between the two sites that was reduced during Hif-1α stabilisation. During systemic Mm infection, wounding leads to increased infection burden, but the protective effect of Hif-1α stabilisation remains. Our data indicate that Hif-1α stabilisation alters neutrophil migration dynamics between comorbid sites and that the protective effect of Hif-1α against Mm is maintained in the presence of inflammation, highlighting its potential as a host-derived target against TB infection.

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.

MxA suppresses TAK1-IKKα/β-NF-κB mediated inflammatory cytokine production to facilitate Mycobacterium tuberculosis infection

OBJECTIVES

Interferons (IFNs) play multifunctional roles in host defense against infectious diseases by inducing IFN-stimulated genes (ISGs). However, little is known about how ISGs regulate host immune response to Mycobacterium tuberculosis (Mtb) infection, the major cause of tuberculosis (TB).

METHODS

We thus profiled the potential effects and mechanisms of eight Mtb-induced ISGs on Mtb infection by RNA interference in human macrophages (Mφs) derived from peripheral blood monocytes (hMDMs) and THP-1 cell line derived Mφs (THP-1-Mφs).

RESULTS

MxA silencing significantly decreased intracellular Mtb infection in Mφs. Mechanistically, MxA silencing promoted inflammatory cytokines IL-1β, IL-6 and TNF-α production, and induced NF-κB p65 activation. Pharmacological inhibition of NF-κB p65 activation or gene silencing of NF-κB p65 blocked the increased production of IL-1β, IL-6 and TNF-α and restored Mtb infection by MxA silencing. Furthermore, pharmacological inhibition of TAK1 and IKKα/β blocked NF-κB p65 activation and subsequent production of pro-inflammatory cytokines by MxA silencing. Isoniazid (INH) treatment and MxA silencing could promote TAK1-IKKα/β-NF-κB signaling pathway activation and combat Mtb infection independently.

CONCLUSIONS

Our results reveal a novel role of MxA in regulating TAK1-IKKα/β-NF-κB signaling activation and production of antimicrobial inflammatory cytokines upon Mtb infection, providing a potential target for clinical treatment of TB.

Immunometabolism during Mycobacterium tuberculosis Infection

Over a quarter of the world's population is infected with Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). Approximately 3.4% of new and 18% of recurrent cases of TB are multidrug-resistant (MDR) or rifampicin-resistant. Recent evidence has shown that certain drug-resistant strains of Mtb modulate host metabolic reprogramming, and therefore immune responses, during infection. However, it remains unclear how widespread these mechanisms are among circulating MDR Mtb strains and what impact drug-resistance-conferring mutations have on immunometabolism during TB. While few studies have directly addressed metabolic reprogramming in the context of drug-resistant Mtb infection, previous literature examining how drug-resistance mutations alter Mtb physiology and differences in the immune response to drug-resistant Mtb provides significant insights into how drug-resistant strains of Mtb differentially impact immunometabolism.

Fish Macrophages Show Distinct Metabolic Signatures Upon Polarization

Macrophages play important roles in conditions ranging from host immune defense to tissue regeneration and polarize their functional phenotype accordingly. Next to differences in the use of L-arginine and the production of different cytokines, inflammatory M1 macrophages and anti-inflammatory M2 macrophages are also metabolically distinct. In mammals, M1 macrophages show metabolic reprogramming toward glycolysis, while M2 macrophages rely on oxidative phosphorylation to generate energy. The presence of polarized functional immune phenotypes conserved from mammals to fish led us to hypothesize that a similar metabolic reprogramming in polarized macrophages exists in carp. We studied mitochondrial function of M1 and M2 carp macrophages under basal and stressed conditions to determine oxidative capacity by real-time measurements of oxygen consumption and glycolytic capacity by measuring lactate-based acidification. In M1 macrophages, we found increased nitric oxide production and irg1 expression in addition to altered oxidative phosphorylation and glycolysis. In M2 macrophages, we found increased arginase activity, and both oxidative phosphorylation and glycolysis were similar to control macrophages. These results indicate that M1 and M2 carp macrophages show distinct metabolic signatures and indicate that metabolic reprogramming may occur in carp M1 macrophages. This immunometabolic reprogramming likely supports the inflammatory phenotype of polarized macrophages in teleost fish such as carp, similar to what has been shown in mammals.

Analysis tools to quantify dissemination of pathology in zebrafish larvae

We describe new open source software called QuantiFish for rapid quantitation of fluorescent foci in zebrafish larvae, to support infection research in this animal model. QuantiFish extends the conventional measurements of bacterial load and number of bacterial foci to include measures for dissemination of infection. These are represented by the proportions of bacteria between foci and their spatial distribution. We showcase these measures by comparison of intravenous and hindbrain routes of Mycobacterium marinum infection, which are indistinguishable by measurement of bacterial load and not consistently differentiated by the number of bacterial foci. The intravenous route showed dose dependent dissemination of infection, reflected by increased spatial dispersion of bacteria and lower proportions of bacteria distributed across many foci. In contrast, hindbrain infection resulted in localised disease, limited to a smaller area and higher proportions of bacteria distributed across fewer foci. The application of QuantiFish may extend beyond models of infection, to study other pathologies such as metastatic cancer.