A novel Cre-enabled tetracycline-inducible transgenic system for tissue-specific cytokine expression in the zebrafish: CETI-PIC3

Leveraging zebrafish to investigate pancreatic development, regeneration, and diabetes

The zebrafish has become an outstanding model for studying organ development and tissue regeneration, which is prominently leveraged for studies of pancreatic development, insulin-producing β-cells, and diabetes. Although studied for more than two decades, many aspects remain elusive and it has only recently been possible to investigate these due to technical advances in transcriptomics, chemical-genetics, genome editing, drug screening, and in vivo imaging. Here, we review recent findings on zebrafish pancreas development, β-cell regeneration, and how zebrafish can be used to provide novel insights into gene functions, disease mechanisms, and therapeutic targets in diabetes, inspiring further use of zebrafish for the development of novel therapies for diabetes.

Inflammation in Development and Aging: Insights from the Zebrafish Model

Zebrafish are an emergent animal model to study human diseases due to their significant genetic similarity to humans, swift development, and genetic manipulability. Their utility extends to the exploration of the involvement of inflammation in host defense, immune responses, and tissue regeneration. Additionally, the zebrafish model system facilitates prompt screening of chemical compounds that affect inflammation. This study explored the diverse roles of inflammatory pathways in zebrafish development and aging. Serving as a crucial model, zebrafish provides insights into the intricate interplay of inflammation in both developmental and aging contexts. The evidence presented suggests that the same inflammatory signaling pathways often play instructive or beneficial roles during embryogenesis and are associated with malignancies in adults.

An inducible model of chronic hyperglycemia

Transgene driven expression of Escherichia coli nitroreductase (NTR1.0) renders animal cells susceptible to the antibiotic metronidazole (MTZ). Many NTR1.0/MTZ ablation tools have been reported in zebrafish, which have significantly impacted regeneration studies. However, NTR1.0-based tools are not appropriate for modeling chronic cell loss as prolonged application of the required MTZ dose (10 mM) is deleterious to zebrafish health. We established that this dose corresponds to the median lethal dose (LD50) of MTZ in larval and adult zebrafish and that it induced intestinal pathology. NTR2.0 is a more active nitroreductase engineered from Vibrio vulnificus NfsB that requires substantially less MTZ to induce cell ablation. Here, we report on the generation of two new NTR2.0-based zebrafish lines in which acute β-cell ablation can be achieved without MTZ-associated intestinal pathology. For the first time, we were able to sustain β-cell loss and maintain elevated glucose levels (chronic hyperglycemia) in larvae and adults. Adult fish showed significant weight loss, consistent with the induction of a diabetic state, indicating that this paradigm will allow the modeling of diabetes and associated pathologies.

Adult zebrafish as advanced models of human disease

Modelling adult diseases to understand their aetiology and progression, and to develop new therapies, is a major challenge for medical biology. We are excited by new efforts in the zebrafish community to develop models of adult diseases that range from cancer to heart, infectious and age-related diseases, and those that relate to toxicology and complex social behaviours. Here, we discuss some of the advances in the field of zebrafish models of adult disease, and where we see opportunities and challenges ahead.

Inside the β Cell: Molecular Stress Response Pathways in Diabetes Pathogenesis

The pathogeneses of the 2 major forms of diabetes, type 1 and type 2, differ with respect to their major molecular insults (loss of immune tolerance and onset of tissue insulin resistance, respectively). However, evidence suggests that dysfunction and/or death of insulin-producing β-cells is common to virtually all forms of diabetes. Although the mechanisms underlying β-cell dysfunction remain incompletely characterized, recent years have witnessed major advances in our understanding of the molecular pathways that contribute to the demise of the β-cell. Cellular and environmental factors contribute to β-cell dysfunction/loss through the activation of molecular pathways that exacerbate endoplasmic reticulum stress, the integrated stress response, oxidative stress, and impaired autophagy. Whereas many of these stress responsive pathways are interconnected, their individual contributions to glucose homeostasis and β-cell health have been elucidated through the development and interrogation of animal models. In these studies, genetic models and pharmacological compounds have enabled the identification of genes and proteins specifically involved in β-cell dysfunction during diabetes pathogenesis. Here, we review the critical stress response pathways that are activated in β cells in the context of the animal models.

Functional identification of the zebrafish Interleukin-1 receptor in an embryonic model of Il-1β-induced systemic inflammation

Interleukin-1β (IL-1β) is a potent proinflammatory cytokine that plays a vital role in the innate immune system. To observe the innate immune response in vivo, several transgenic zebrafish lines have been developed to model IL-1β-induced inflammation and to visualize immune cell migration and proliferation in real time. However, our understanding of the IL-1β response in zebrafish is limited due to an incomplete genome annotation and a lack of functional data for the cytokine receptors involved in the inflammatory process. Here, we use a combination of database mining, genetic analyses, and functional assays to identify zebrafish Interleukin-1 receptor, type 1 (Il1r1). We identified putative zebrafish il1r1 candidate genes that encode proteins with predicted structures similar to human IL1R1. To examine functionality of these candidates, we designed highly effective morpholinos to disrupt gene expression in a zebrafish model of embryonic Il-1β-induced systemic inflammation. In this double transgenic model, ubb:Gal4-EcR, uas:il1βmat , the zebrafish ubiquitin b (ubb) promoter drives expression of the modified Gal4 transcription factor fused to the ecdysone receptor (EcR), which in turn drives the tightly-regulated expression and secretion of mature Il-1β only in the presence of the ecdysone analog tebufenozide (Teb). Application of Teb to ubb:Gal4-EcR, uas:il1βmat embryos causes premature death, fin degradation, substantial neutrophil expansion, and generation of reactive oxygen species (ROS). To rescue these deleterious phenotypes, we injected ubb:Gal4-EcR, uas:il1βmat embryos with putative il1r1 morpholinos and found that knockdown of only one candidate gene prevented the adverse effects caused by Il-1β. Mosaic knockout of il1r1 using the CRISPR/Cas9 system phenocopied these results. Taken together, our study identifies the functional zebrafish Il1r1 utilizing a genetic model of Il-1β-induced inflammation and provides valuable new insights to study inflammatory conditions specifically driven by Il-1β or related to Il1r1 function in zebrafish.

Macrophages and neutrophils are necessary for ER stress-induced β cell loss

Persistent endoplasmic reticulum (ER) stress induces islet inflammation and β cell loss. How islet inflammation contributes to β cell loss remains uncertain. We have reported previously that chronic overnutrition-induced ER stress in β cells causes Ripk3-mediated islet inflammation, macrophage recruitment, and a reduction of β cell numbers in a zebrafish model. We show here that β cell loss results from the intricate communications among β cells, macrophages, and neutrophils. Macrophage-derived Tnfa induces cxcl8a in β cells. Cxcl8a, in turn, attracts neutrophils to macrophage-contacted “hotspots” where β cell loss occurs. We also show potentiation of chemokine expression in stressed mammalian β cells by macrophage-derived TNFA. In Akita and db/db mice, there is an increase in CXCL15-positive β cells and intra-islet neutrophils. Blocking neutrophil recruitment in Akita mice preserves β cell mass and slows diabetes progression. These results reveal an important role of neutrophils in persistent ER stress-induced β cell loss.

Yang et al. show a pivotal role of communications among β cells, macrophages, and neutrophils in chronic overnutrition-induced loss of pancreatic β cells in a diabetes-prone zebrafish model.

Modelling infectious disease to support human health

During the current COVID-19 pandemic, there has been renewed scientific and public focus on understanding the pathogenesis of infectious diseases and investigating vaccines and therapies to combat them. In addition to the tragic toll of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), we also recognize increased threats from antibiotic-resistant bacterial strains, the effects of climate change on the prevalence and spread of human pathogens, and the recalcitrance of other infectious diseases – including tuberculosis, malaria, human immunodeficiency virus (HIV) and fungal infections – that continue to cause millions of deaths annually. Large amounts of funding have rightly been redirected toward vaccine development and clinical trials for COVID-19, but we must continue to pursue fundamental and translational research on other pathogens and host immunity. Now more than ever, we need to support the next generation of researchers to develop and utilize models of infectious disease that serve as engines of discovery, innovation and therapy.

Summary: This Editorial considers how knowledge from animal and other models of infectious disease can impact our understanding of human biology and potential therapies, focusing largely on zebrafish. It also highlights ways in which DMM is supporting these areas.

A Novel 2-Hit Zebrafish Model to Study Early Pathogenesis of Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases in adults. NAFLD progresses from benign liver fat accumulation to liver inflammation and cirrhosis, and ultimately leads to liver failure. Although several rodent models have been established for studying NAFLD, they have limitations that include cost, speed of disease development, key dissimilarities, and poor amenability to pharmacological screens. Here, we present a novel 2-hit zebrafish model to replicate aspects of NAFLD pathogenesis. We fed zebrafish larvae a high-fat diet (HFD) to drive liver fat accumulation (first hit). Next, we exacerbated liver-specific inflammation using a transgenic line (fabp10-CETI-PIC3) that induces the expression of proinflammatory cytokines following induction with doxycycline (second hit). These hits promoted fat accumulation and liver inflammation, as demonstrated by the high expression of inflammatory cytokines, macrophage infiltration, stress induction, and hepatic lipid droplet accumulation. Furthermore, zebrafish in this paradigm showed deranged glucose metabolism. To validate a small-molecule screening approach, we treated HFD-fed fish with pioglitazone, a drug shown to be beneficial for NAFLD in humans, and measured a sharp reduction in liver lipid accumulation. These results demonstrate new utility for zebrafish in modeling early NAFLD pathogenesis and demonstrate their feasibility for in vivo screening of new pharmacological interventions.

Genetically inducible and reversible zebrafish model of systemic inflammation

The inflammatory response is a vital defense mechanism against trauma and pathogen induced damage, but equally important is its appropriate resolution. In some instances of severe trauma or sustained infection, inappropriate and persistent activation of the immune response can occur resulting in a dangerous systemic inflammatory response. Untreated, this systemic inflammatory response can lead to tissue damage, organ shutdown, and death. Replicating this condition in tractable model organisms can provide insight into the mechanisms involved in the induction, maintenance, and resolution of inflammation. To that end, we developed a non-invasive, inducible, and reversible model of systemic inflammation in zebrafish. Using the Gal4-EcR/UAS system activated by the ecdysone analog tebufenozide, we generated transgenic zebrafish that allow for chemically-induced, ubiquitous secretion of the mature form of zebrafish interleukin-1β (Il-1βmat) in both larval and adult developmental stages. To ensure a robust immune response, we attached a strong signal peptide from the Gaussia princeps luciferase enzyme to promote active secretion of the cytokine. We observe a dose-dependent inflammatory response involving neutrophil expansion accompanied by tissue damage and reduced survival. Washout of tebufenozide permits inflammation resolution. We also establish the utility of this model for the identification of small molecule anti-inflammatory compounds by treatment with the immunosuppressant rapamycin. Taken together, these features make this model a valuable new tool that can aid in identifying potential new therapies while broadening our understanding of systemic inflammation, its impact on the immune system and its resolution.

What lies beyond 100 years of insulin

It has been 100 years since the discovery of insulin. This revolutionary treatment saves the lives of millions of people living with diabetes, but much remains to be understood of its mechanisms and roles in homeostasis and disease. To celebrate this centenary, we explore areas of ongoing insulin research in diabetes, metabolic syndrome and beyond. Disease Models & Mechanisms aims to publish high-quality basic and pre-clinical research that advances our understanding of these conditions to facilitate clinical and public health impact.

First person – Sara Ibrahim

First Person is a series of interviews with the first authors of a selection of papers published in Disease Models & Mechanisms, helping early-career researchers promote themselves alongside their papers. Sara Ibrahim is first author on ‘A novel Cre-enabled tetracycline-inducible transgenic system for tissue-specific cytokine expression in the zebrafish: CETI-PIC3’, published in DMM. Sara is an MD-PhD student in the lab of Emily K. Sims and Ryan M. Anderson at Indiana University School of Medicine, Indianapolis, IN, USA, developing and utilizing molecular biology techniques to study β cell dysfunction.