Dynamic glucoregulation and mammalian-like responses to metabolic and developmental disruption in zebrafish

Treatment of overactive KATP channels with glibenclamide in a zebrafish model and a clinical trial in humans with Cantú syndrome

This study explores the efficacy of glibenclamide, a KATP channel inhibitor, for treating Cantú syndrome (CS), a genetic disorder characterized by hypertrichosis and cardiovascular abnormalities. Treatment with glibenclamide for Cantú syndrome has only been reported in a single case report. In this study, we tested this repurposed drug in both a zebrafish model and an open-label trial with CS patients. CS zebrafish embryos, created using CRISPR/Cas9, were treated with glibenclamide. Their cardiac function was assessed using high-speed imaging. In the trial part of the study, four adults with CS used 2.5 mg glibenclamide daily for 8 months. Hypertrichosis, cardiac function, and edema were evaluated and glucose levels were monitored continuously. In the zebrafish model of CS glibenclamide reversed cardiac abnormalities. However, in the clinical trial, the effects on hypertrichosis were mixed, and there were no significant changes in cardiac phenotype or leg edema. One participant reported reduced facial erythema and puffiness, which relapsed post-trial. The treatment was generally safe, with multiple instances of level 1 hypoglycemia but no severe adverse events. In conclusion, glibenclamide can reverse cardiac abnormalities in a CS zebrafish model. Its effect on hypertrichosis and cardiovascular features in humans with CS are unclear and dosage increases are challenging due to hypoglycemia, which is important knowledge for treatment considerations in this rare genetic syndrome.Trial registration: EudraCT Number 2019-004651-36. Date of first registration 21/05/2021.

Depolymerization of oyster glycosaminoglycans for the enhancement of α-glucosidase inhibition and its application in hypoglycemic studies

Glycosaminoglycans are a class of naturally occurring macromolecular heteropolysaccharides with α-glucosidase inhibitory effects, which play an essential role in regulating postprandial hyperglycemia. However, the significant molecular weight hinders their inhibitory activity. In this study, oyster glycosaminoglycans were used for purification and depolymerization studies to obtain oyster glycosaminoglycan oligosaccharides (OGAG-Oli) and to study their inhibitory activity against α-glucosidase in vitro and hypoglycemic effect on hyperglycemic zebrafish in vivo. The results showed that the OGAG-Oli with optimal α-glucosidase inhibition obtained by the β-elimination mechanism of chondroitinase ABC had a molecular weight of about 2400 Da with five disaccharide repeating units, and their inhibitory effect on α-glucosidase was significantly enhanced with an IC50 value of 0.12 mg/mL, which was related to the strong binding capacity with α-glucosidase as evidenced by molecular docking. FT-IR and NMR results showed that the conformation of OGAG-Oli was predominantly in the α-configuration, which indicated that its inhibitory effect on α-glucosidase mainly depended on the α-glucosidic bond therein. The enzymatic depolymerization process of glycosaminoglycans was optimized, and the process conditions were determined as phosphate buffer solution pH 8.0, reaction time 3 h, reaction temperature 30 °C, chondroitin enzyme ABC activity 0.5 mU. The hypoglycemic ability of OGAG-Oli was evaluated in diabetic zebrafish, and the results showed that OGAG-Oli at a high-dose (0.12 mg/g, bw/d) could extremely significantly reduce fasting blood glucose in zebrafish, with an effect close to that of acarbose (p > 0.05), and exceptionally significantly (p < 0.01) reduced the elevation of TC, TG, and LDL-C caused by prolonged hyperglycemia, and extremely significantly (p < 0.01) increased the HDL-C level. This study showed that the structurally modified oyster glycosaminoglycans had intense α-glucosidase inhibitory activity, and exhibited biological activity of reducing glucose uptake and consequently improving body weight and lipid metabolism in diabetic zebrafish. As a bioactive ingredient of natural origin, this study provides a theoretical basis for the development and utilization of glycosaminoglycans with hypoglycemic effects in foods and drugs.

Conserved glucokinase regulation in zebrafish confirms therapeutic utility for pharmacologic modulation in diabetes

Glucokinase (GCK) is an essential enzyme for blood glucose homeostasis. Because of its importance in glucose metabolism, GCK is considered an attractive target for the development of antidiabetic drugs. However, a viable therapeutic agent has still to emerge, prompting efforts to improve understanding of the complex regulation and biological effects of GCK. Using the vertebrate organism zebrafish, an attractive model to study metabolic diseases and pharmacological responses, we dissected the complexities of gck regulation and unraveled effects of Gck modulation. We found that while gck expression in zebrafish islet cells is constitutive, gck expression in the liver is regulated by nutritional status, confirming similarity to the mammalian system. A combination of transgenic gck reporter lines and our diabetes model, the pdx1 mutant, allowed monitoring of gck expression under pathological conditions, revealing reduced gck expression and activity in the liver, which was unresponsive to nutrient stimulation, and decreased expression in the islet due to the reduced number of β-cells. Gck activation substantially ameliorated hyperglycemia in pdx1 mutants, without inducing oxidative stress responses in liver or islet. In-depth characterization of Gck activity and regulation at the cellular level in a whole-organism diabetes model clarifies its applicability as a drug target for therapies.

Gluconeogenesis during development of the grass puffer (Takifugu niphobles)

During the development of teleost fish, the sole nutrient source is the egg yolk. The yolk consists mostly of proteins and lipids, with only trace amounts of carbohydrates such as glycogen and glucose. However, past evidence in some fishes showed transient increase in glucose during development, which may have supported the development of the embryos. Recently, we found in zebrafish that the yolk syncytial layer (YSL), an extraembryonic tissue surrounding the yolk, undergoes gluconeogenesis. However, in other teleost species, the knowledge on such gluconeogenic functions during early development is lacking. In this study, we used a marine fish, the grass puffer (Takifugu niphobles) and assessed possible gluconeogenic functions of their YSL, to understand the difference or shared features of gluconeogenesis between these species. A liquid chromatography (LC) / mass spectrometry (MS) analysis revealed that glucose and glycogen content significantly increased in the grass puffer during development. Subsequent real-time PCR results showed that most of the genes involved in gluconeogenesis increased in segmentation stages and/or during hatching. Among these genes, many were expressed in the YSL and liver, as shown by in situ hybridization analysis. In addition, glycogen immunostaining revealed that this carbohydrate source was accumulated in many tissues at segmentation stage but exclusively in the liver in hatched individuals. Taken together, these results suggest that developing grass puffer undergoes gluconeogenesis and glycogen synthesis during development, and that gluconeogenic activity is shared in YSL of zebrafish and grass puffer.

Stilbenoids from fenugreek seeds alleviate insulin resistance by regulating the PI3K/AKT/mTOR signaling pathway in a type 2 diabetes zebrafish model

Insulin resistance (IR) is the main cause of type 2 diabetes mellitus (T2DM). The specific targets and underlying mechanisms responsible for the ameliorative effects of the stilbenoid compounds found in fenugreek seeds for ameliorating IR require further study. Here, we were predicted by using the network pharmacology prediction, molecular docking and molecular dynamics simulation approach the targets in common and the potential mechanismsof three stilbenoid compounds (rhaponticin, desoxyrhaponticin, and rhapontigenin) in relation to T2DM and IR. The results showed that the compounds may improve IR through the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway. Molecular docking studies revealed that they exhibit high binding affinity with the structural domains of peroxisome proliferator-activated receptor gamma (PPARG), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), PI3K, and AKT. These results suggest that PPARG and GAPDH may be the potential targets for these three compounds in the treatment of T2DM.Subsequently, experiments using the zebrafish T2DM model showed that the stilbenoid compounds had varying degrees of efficacy in improving IR through the PI3K/AKT/mTOR signaling pathway, and rhaponticin had the most promising effects. The findings implicate a potential mechanism of action for the three stilbenoid compounds in enhancing insulin resistance (IR) through modulation of the PI3K/AKT/mTOR pathway.

Characterization of the zebrafish as a model of ATP-sensitive potassium channel hyperinsulinism

INTRODUCTION

Congenital hyperinsulinism (HI) is the leading cause of persistent hypoglycemia in infants. Current models to study the most common and severe form of HI resulting from inactivating mutations in the ATP-sensitive potassium channel (KATP) are limited to primary islets from patients and the Sur1 -/- mouse model. Zebrafish exhibit potential as a novel KATPHI model since they express canonical insulin secretion pathway genes and those with identified causative HI mutations. Moreover, zebrafish larvae transparency provides a unique opportunity for in vivo visualization of pancreatic islets.

RESEARCH DESIGN AND METHODS

We evaluated zebrafish as a model for KATPHI using a genetically encoded Ca2+ sensor (ins:gCaMP6s) expressed under control of the insulin promoter in beta cells of an abcc8 -/- zebrafish line.

RESULTS

We observed significantly higher islet cytosolic Ca2+ in vivo in abcc8 -/- compared with abcc8 +/+ zebrafish larvae. Additionally, abcc8 -/- larval zebrafish had significantly lower whole body glucose and higher whole body insulin levels compared with abcc8 +/+ controls. However, adult abcc8 -/- zebrafish do not show differences in plasma glucose, plasma insulin, or glucose tolerance when compared with abcc8 +/+ zebrafish.

CONCLUSIONS

Our results identify that zebrafish larvae, but not adult fish, are a demonstrable novel model for advancement of HI research.

Gluconeogenesis in the extraembryonic yolk syncytial layer of the zebrafish embryo

Yolk-consuming (lecithotrophic) embryos of oviparous animals, such as those of fish, need to make do with the maternally derived yolk. However, in many cases, yolk possesses little carbohydrates and sugars, including glucose, the essential monosaccharide. Interestingly, increases in the glucose content were found in embryos of some teleost fishes; however, the origin of this glucose has been unknown. Unveiling new metabolic strategies in fish embryos has a potential for better aquaculture technologies. In the present study, using zebrafish, we assessed how these embryos obtain the glucose. We employed stable isotope (13C)-labeled substrates and injected them to the zebrafish embryos. Our liquid chromatography-mass spectrometry-based isotope tracking revealed that among all tested substrate, glutamate was most actively metabolized to produce glucose in the zebrafish embryos. Expression analysis for gluconeogenic genes found that many of these were expressed in the yolk syncytial layer (YSL), an extraembryonic tissue found in teleost fishes. Generation 0 (G0) knockout of pck2, a gene encoding the key enzyme for gluconeogenesis from Krebs cycle intermediates, reduced gluconeogenesis from glutamate, suggesting that this gene is responsible for gluconeogenesis from glutamate in the zebrafish embryos. These results showed that teleost YSL undergoes gluconeogenesis, likely contributing to the glucose supplementation to the embryos with limited glucose source. Since many other animal lineages lack YSL, further comparative analysis will be interesting.

Multivalent insulin receptor activation using insulin-DNA origami nanostructures

Insulin binds the insulin receptor (IR) and regulates anabolic processes in target tissues. Impaired IR signalling is associated with multiple diseases, including diabetes, cancer and neurodegenerative disorders. IRs have been reported to form nanoclusters at the cell membrane in several cell types, even in the absence of insulin binding. Here we exploit the nanoscale spatial organization of the IR to achieve controlled multivalent receptor activation. To control insulin nanoscale spatial organization and valency, we developed rod-like insulin-DNA origami nanostructures carrying different numbers of insulin molecules with defined spacings. Increasing the insulin valency per nanostructure markedly extended the residence time of insulin-DNA origami nanostructures at the receptors. Both insulin valency and spacing affected the levels of IR activation in adipocytes. Moreover, the multivalent insulin design associated with the highest levels of IR activation also induced insulin-mediated transcriptional responses more effectively than the corresponding monovalent insulin nanostructures. In an in vivo zebrafish model of diabetes, treatment with multivalent-but not monovalent-insulin nanostructures elicited a reduction in glucose levels. Our results show that the control of insulin multivalency and spatial organization with nanoscale precision modulates the IR responses, independent of the insulin concentration. Therefore, we propose insulin nanoscale organization as a design parameter in developing new insulin therapies.

Adverse effects of plastic leachate and its component 2,4-DTBP on the early development of zebrafish embryos

Plastic waste has become a global environmental problem threatening the health of aquatic organisms especially via leachate. In this study, the test of zebrafish embryo showed adverse effects of leachate from some agricultural mulching films after UV light aging for 60 h. A typical phenolic antioxidant 2,4-di-tert-butylphenol (2,4-DTBP) was detected in the leachate and tested further for the zebrafish embryo biotoxicity. The microplastic leachate (6, 8 g/L, mass concentration measured by weight of plastic) increased the death and malformation rates, and reduced the hatching rate, heart rate, and body length of zebrafish larvae in the 96-hour early development period. Similar adverse effects were also caused by the 2,4-DTBP (0.01, 0.1, 1.0 mg/L, corresponding to 0.049, 0.49, and 4.85 μM) to some degree but could not completely explain the significant influences caused by the plastic leachate. Transcriptome analysis of zebrafish embryos exposed to the 2,4-DTBP for 96 h showed that the protein, fat, and carbohydrate digestion and absorption pathways, pancreatic secretion, PPAR signaling pathway, tryptophan metabolism, and adipocytokine signaling pathway were considerably down-regulated, but the cholesterol metabolism pathway was up-regulated in larval zebrafish. The altered transcriptional expression of mRNA at early development stage (96 h post fertilization) of zebrafish suggested that the 2,4-DTBP caused reduction of digestive capacity and pancreatic secretory function, and adversely affected processes associated with energy metabolism and glycolipid metabolism of larval zebrafish. This study helps us further understanding the effects of plastic leachate on the early development of fishes.

Reversible Recognition-Based Boronic Acid Probes for Glucose Detection in Live Cells and Zebrafish

Glucose, a critical source of energy, directly determines the homeostasis of the human body. However, due to the lack of robust imaging probes, the mechanism underlying the changes of glucose homeostasis in the human body remains unclear. Herein, diboronic acid probes with good biocompatibility and high sensitivity were synthesized based on an ortho-aminomethylphenylboronic acid probe, phenyl(di)boronic acid (PDBA). Significantly, by introducing the water-solubilizing group -CN directly opposite the boronic acid group and -COOCH₃ or -COOH groups to the β site of the anthracene in PDBA, we obtained the water-soluble probe Mc-CDBA with sensitive response (F/F₀ = 47.8, detection limit (LOD) = 1.37 μM) and Ca-CDBA with the highest affinity for glucose (K_a = 4.5 × 10³ M^-1). On this basis, Mc-CDBA was used to identify glucose heterogeneity between normal and tumor cells. Finally, Mc-CDBA and Ca-CDBA were used for imaging glucose in zebrafish. Our research provides a new strategy for designing efficient boronic acid glucose probes and powerful new tools for the evaluation of glucose-related diseases.

Research Progress on the Construction and Application of a Diabetic Zebrafish Model

Diabetes is a metabolic disease characterized by high blood glucose levels. With economic development and lifestyle changes, the prevalence of diabetes is increasing yearly. Thus, it has become an increasingly serious public health problem in countries around the world. The etiology of diabetes is complex, and its pathogenic mechanisms are not completely clear. The use of diabetic animal models is helpful in the study of the pathogenesis of diabetes and the development of drugs. The emerging vertebrate model of zebrafish has many advantages, such as its small size, large number of eggs, short growth cycle, simple cultivation of adult fish, and effective improvement of experimental efficiency. Thus, this model is highly suitable for research as an animal model of diabetes. This review not only summarizes the advantages of zebrafish as a diabetes model, but also summarizes the construction methods and challenges of zebrafish models of type 1 diabetes, type 2 diabetes, and diabetes complications. This study provides valuable reference information for further study of the pathological mechanisms of diabetes and the research and development of new related therapeutic drugs.

Regenerative potential and limitations in a zebrafish model of hyperglycemia-induced nerve degeneration

BACKGROUND

Previous work from our lab has described a model of motor nerve degeneration in hyperglycemic zebrafish larvae which resembles mammalian models of diabetic peripheral neuropathy (DPN). Here, we optimized the hyperglycemic-induction protocol, characterized deficits in nerve structure and behavioral function, and then examined the regenerative potential following recovery from the hyperglycemic state.

RESULTS

In agreement with our previous work, hyperglycemia induced motor nerve degeneration and behavioral deficits. However, the optimized protocol initiated disruption of tight junctions within the blood-nerve barrier, a phenotype apparent in mammalian models of DPN. Following a 10-day recovery period, regeneration of motor nerve components was apparent, but behavioral deficits persisted. We next examined the effect of hyperglycemia on the musculoskeletal system and found subtle deficits in muscle that resolved following recovery, and robust deficits in the skeletal system which persisted following recovery.

CONCLUSION

Here we optimized our previous model of hyperglycemia-induced motor nerve degeneration to more closely align with that observed in mammalian models and then characterized the regenerative potential following recovery from hyperglycemia. Notably, we observed striking impairments to skeletal development, which underscores the global impact hyperglycemia has across systems, and provides a framework for elucidating molecular mechanisms responsible for regenerative events moving forward.

Advances in Zebrafish for Diabetes Mellitus with Wound Model

Diabetic foot ulcers cause great suffering and are costly for the healthcare system. Normal wound healing involves hemostasis, inflammation, proliferation, and remodeling. However, the negative factors associated with diabetes, such as bacterial biofilms, persistent inflammation, impaired angiogenesis, inhibited cell proliferation, and pathological scarring, greatly interfere with the smooth progress of the entire healing process. It is this impaired wound healing that leads to diabetic foot ulcers and even amputations. Therefore, drug screening is challenging due to the complexity of damaged healing mechanisms. The establishment of a scientific and reasonable animal experimental model contributes significantly to the in-depth research of diabetic wound pathology, prevention, diagnosis, and treatment. In addition to the low cost and transparency of the embryo (for imaging transgene applications), zebrafish have a discrete wound healing process for the separate study of each stage, resulting in their potential as the ideal model animal for diabetic wound healing in the future. In this review, we examine the reasons behind the delayed healing of diabetic wounds, systematically review various studies using zebrafish as a diabetic wound model by different induction methods, as well as summarize the challenges and improvement strategies which provide references for establishing a more reasonable diabetic wound zebrafish model.

Development of a Zebrafish Larvae Model for Diabetic Heart Failure With Reduced Ejection Fraction

BACKGROUND AND OBJECTIVES

Diabetes mellitus (DM)-associated heart failure (HF) causes high morbidity and mortality. In this study, we established a zebrafish larvae model for in vivo research on diabetic HF.

METHODS

DM-like phenotypes were induced by treating zebrafish larvae with a combination of D-glucose (GLU) and streptozotocin (STZ). HF was induced by treatment with terfenadine (TER), a potassium channel blocker. Additionally, myocardial contractility, motility, and viability were evaluated.

RESULTS

The zebrafish larvae treated with a combination of GLU and STZ showed significantly higher whole-body glucose concentrations, lower insulin levels, and higher phosphoenolpyruvate carboxykinase levels, which are markers of abnormal glucose homeostasis, than the group treated with only GLU, with no effect on viability. When treated with TER, DM zebrafish showed significantly less myocardial fractional shortening and more irregular contractions than the non-DM zebrafish. Furthermore, in DM-HF with reduced ejection fraction (rEF) zebrafish, a significant increase in the levels of natriuretic peptide B, a HF biomarker, markedly reduced motility, and reduced survival rates were observed.

CONCLUSIONS

We established a DM-HFrEF zebrafish model by sequentially treating zebrafish larvae with GLU, STZ, and TER. Our findings indicate the potential utility of the developed zebrafish larvae model not only in screening studies of new drug candidates for DM-HFrEF but also in mechanistic studies to understand the pathophysiology of DM-HFrEF.

DNA methylation of pck1 might contribute to the programming effects of early high-carbohydrate diets feeding to the glucose metabolism across two generations in zebrafish (Danio rerio)

The purpose of this study is to assess the effects of early high-carbohydrate stimulus on glucose metabolism in zebrafish (Danio rerio) over two generations and explore the mechanisms that explain those nutritional programming effects via epigenetic modifications. The larvae were delivered a high-carbohydrate diet (53.66%) that was used as an early nutritional stimulus from the first feeding to the end of the yolk sac (FF) and 5 days after yolk-sac exhaustion (YE). The larvae (F0) and their offspring (F1) were then both fed the control diet (22.69%) until adulthood (15 weeks), and they were challenged with a high-carbohydrate diet (35.36%) at the 16th week. The results indicated that early stimulus immediately raised the mRNA levels of genes involved in glycolysis and gluconeogenesis. At the end of F0 challenge, both treatment groups decreased the plasma glucose levels, increased the expression levels of glucokinase (gck), and inhibited the mRNA during gluconeogenesis. When challenged in F1, the glucose levels were lower in FF (F1), and the mRNA levels of phosphoenolpyruvate carboxykinase 1 (pck1) were decreased in FF (F1) and YE (F1). Besides, in both experimental groups (F0 and F1), the CpG island of pck1 maintained lower levels of hypermethylated expression from F0 adult, 24 h post-fertilization embryo, to F1 adult. In conclusion, these results indicated that an early high-carbohydrate stimulus could significantly reprogram glucose metabolism in adult zebrafish, that those modifications could be partially transmitted to the next generation, and that the DNA methylation of pck1 might work as a stable epigenetic marker to contribute to those processes.

Nitrate exposure reprograms hepatic amino acid and nutrient sensing pathways prior to exercise: A metabolomic and transcriptomic investigation in zebrafish (Danio rerio)

Scope: Nitrate supplementation is a popular ergogenic aid that improves exercise performance by reducing oxygen consumption during exercise. We investigated the effect of nitrate exposure and exercise on metabolic pathways in zebrafish liver.

Materials and methods: Fish were exposed to sodium nitrate (606.9 mg/L), or control water, for 21 days and analyzed at intervals during an exercise test. We utilized untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis and measured gene expression of 24 genes central to energy metabolism and redox signaling.

Results: We observed a greater abundance of metabolites involved in endogenous nitric oxide (NO) metabolism and amino acid metabolism in nitrate-treated liver at rest, compared to rested controls. In the absence of exercise, nitrate treatment upregulated expression of genes central to nutrient sensing (pgc1a), protein synthesis (mtor) and purine metabolism (pnp5a and ampd1) and downregulated expression of genes involved in mitochondrial fat oxidation (acaca and cpt2).

Conclusion: Our data support a role for sub-chronic nitrate treatment in the improvement of exercise performance, in part, by improving NO bioavailability, sparing arginine, and modulating hepatic gluconeogenesis and glycolytic capacity in the liver.

Tpo knockout in zebrafish partially recapitulates clinical manifestations of congenital hypothyroidism and reveals the involvement of TH in proper development of glucose homeostasis

Congenital hypothyroidism (CH) is a highly prevalent but treatable neonatal endocrine disorder. Thyroid peroxidase (TPO) catalyzes key reactions in thyroid hormone (TH) synthesis. TPO mutations have been found to underlie approximately 5% of congenital hypothyroidism in Chinese patients with more severe phenotypes, the treatment of whom usually requires a higher dose of L-thyroxine. The Tpo gene of zebrafish has 66% homology with the human TPO gene, and synteny analysis has indicated that it is likely a human TPO ortholog. In this study, we generated a tpo^-/- mutant zebrafish line through knockout of tpo with CRISPR/Cas9 and investigated the associated phenotypes. Tpo^-/- mutant zebrafish displayed growth retardation; an increased number of thyroid follicular cells; and abnormal extrathyroidal phenotypes including pigmentation defects, erythema in the thoracic region, delayed scale development and failure of swim bladder secondary lobe formation. All these abnormal phenotypes were reversed by 30 nM thyroxine (T4) treatment starting at 1 month of age. Tpo^-/- mutants also showed increased glucose levels during larval stages, and the increases were induced at least in part by increasing glucagon and decreasing insulin expression. Our work indicates that tpo-mutant zebrafish may serve as a human congenital hypothyroidism model for studying TPO- and TH-related disease mechanisms.

High glucose-induced ROS-accumulation in embryo-larval stages of zebrafish leads to mitochondria-mediated apoptosis

In recent decades, diabetes mellitus has become a major chronic disease threatening human health worldwide, and the age of patients tends to be younger; however, the pathogenesis remains unclear, resulting in many difficulties in its treatment. As an ideal model animal, zebrafish can simulate the processes of human diabetes well. In this study, we successfully established a model of diabetic zebrafish larvae in a previous work. Furthermore, transcriptome analysis was completed, and the results suggested that 10.59% of differentially expressed genes (DEGs) related to the apoptosis pathway need to be considered. Then, glucose-induced developmental toxicity, reactive oxygen species (ROS) accumulation, antioxidant system function, apoptosis and mitochondrial dysfunction were measured in zebrafish larvae. We hope that this study will provide valuable reference information for type 2 juvenile diabetes treatment.

Differential Responses of Neural Retina Progenitor Populations to Chronic Hyperglycemia

Diabetic retinopathy is a frequent complication of longstanding diabetes, which comprises a complex interplay of microvascular abnormalities and neurodegeneration. Zebrafish harboring a homozygous mutation in the pancreatic transcription factor pdx1 display a diabetic phenotype with survival into adulthood, and are therefore uniquely suitable among zebrafish models for studying pathologies associated with persistent diabetic conditions. We have previously shown that, starting at three months of age, pdx1 mutants exhibit not only vascular but also neuro-retinal pathologies manifesting as photoreceptor dysfunction and loss, similar to human diabetic retinopathy. Here, we further characterize injury and regenerative responses and examine the effects on progenitor cell populations. Consistent with a negative impact of hyperglycemia on neurogenesis, stem cells of the ciliary marginal zone show an exacerbation of aging-related proliferative decline. In contrast to the robust Müller glial cell proliferation seen following acute retinal injury, the pdx1 mutant shows replenishment of both rod and cone photoreceptors from slow-cycling, neurod-expressing progenitors which first accumulate in the inner nuclear layer. Overall, we demonstrate a diabetic retinopathy model which shows pathological features of the human disease evolving alongside an ongoing restorative process that replaces lost photoreceptors, at the same time suggesting an unappreciated phenotypic continuum between multipotent and photoreceptor-committed progenitors.

In Vivo Toxicity Evaluation of Sugar Adulterated Heterotrigona itama Honey Using Zebrafish Model

Honey is prone to be adulterated through mixing with sugars, cheap and low-quality honey, and other adulterants. Consumption of adulterated honey may cause several health issues such as weight gain, diabetes, and liver and kidney dysfunction. Therefore, studying the impact of consumption of adulterated honey on consumers is critical since there is a lack of study in this field. Hence, the aims of this paper were: (1) to determine the lethal concentration (LC₅₀) of adulterated honey using zebrafish embryo, (2) to elucidate toxicology of selected adulterated honey based on lethal dose (LD₅₀) using adult zebrafish, (3) to determine the effects of adulterated honey on histological changes of zebrafish, and (4) to screen the metabolites profile of adulterated honey by using zebrafish blood serum. The LC₅₀ of Heterotrigona itama honey (acacia honey) and its sugar adulterants (light corn sugar, cane sugar, inverted sugar, and palm sugar in the proportion of 1-3% (w/w) from the total volume) was determined by the toxicological assessment of honey samples on zebrafish embryos (different exposure concentrations in 24, 48, 72, and 96 h postfertilization (hpf)). Pure H. itama honey represents the LC₅₀ of 34.40 ± 1.84 (mg/mL) at 96 hpf, while the inverted sugar represents the lowest LC₅₀ (5.03 ± 0.92 mg/mL) among sugar adulterants. The highest concentration (3%) of sugar adulterants were used to study the toxicology of adulterated honey using adult zebrafish in terms of acute, prolong-acute, and sub-acute tests. The results of the LD₅₀ from the sub-acute toxicity test of pure H. itama honey was 2.33 ± 0.24 (mg/mL). The histological studies of internal organs showed a lesion in the liver, kidney, and spleen of adulterated treated-honey groups compared to the control group. Furthermore, the LC-MS/MS results revealed three endogenous metabolites in both the pure and adulterated honey treated groups, as follows: (1) S-Cysteinosuccinic acid, (2) 2,3-Diphosphoglyceric acid, and (3) Cysteinyl-Tyrosine. The results of this study demonstrated that adulterated honey caused mortality, which contributes to higher toxicity, and also suggested that the zebrafish toxicity test could be a standard method for assessing the potential toxicity of other hazardous food additives. The information gained from this research will permit an evaluation of the potential risk associated with the consumption of adulterated compared to pure honey.

Hypoglycemic Activity of Aqueous Extract of Latex from Hancornia speciosa Gomes: A Study in Zebrafish and In Silico

Hancornia speciosa Gomes is a tree native to Brazil and has therapeutic potential for several diseases. Ethnopharmacological surveys have reported that the plant is used as a hypoglycemic agent and to lose weight. This study aimed to evaluate the effects of the aqueous extract from H. speciosa latex (LxHs) in a zebrafish model of diabetes. The extract was evaluated through high-performance thin-layer chromatography (HTPLC), nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FT-IR). We then tested treatments with LxHs (500, 1000, and 1500 mg/kg) by assessing blood glucose levels in alloxan-induced diabetic animals, and metformin was used as a control. The toxicity was evaluated through histopathology of the pancreas and biochemical assessment of serum levels of AST, ALT, creatinine, and urea. The extract was also assessed for acute toxicity through several parameters in embryos and adult animals. Finally, we performed in silico analysis through the SEA server and docking using the software GOLD. The phytochemical study showed the compounds cornoside, dihydrocornoide, and 1-O-methyl-myoinositol (bornesitol). The treatment with all doses of LxHs significantly decreased alloxan-induced hyperglycemia without any significant histological or biochemical abnormalities. No significant frequency of teratogenesis was observed in the embryos exposed to the extract, and no significant behavioral changes or deaths were observed in adult animals. In silico, the results showed a potential interaction between inositol and enzymes involved in carbohydrates’ metabolism. Overall, the results show a hypoglycemic activity of the extract in vivo, with no apparent toxicity. The computational studies suggest this could be at least partially due to the presence of bornesitol, since inositols can interact with carbohydrates’ enzymes.

Synthesis of disaccharide modified berberine derivatives and their anti-diabetic investigation in zebrafish using a fluorescence-based technology

Berberine is a naturally occurring isoquinoline alkaloid and has been used as an important functional food additive in China due to its various pharmacological activities. Berberine exhibits great potential for developing anti-diabetic agents against type 2 diabetes mellitus (T2DM), as it can reduce the blood glucose level in many animal models. However, the low anti-diabetic activity and poor bioavailability of berberine (below 5%) by oral administration significantly limit its practical applications. To solve these problems, this article focuses on the structural modification of berberine using some disaccharide groups, because the carbohydrate moiety has been proved to improve the bioavailability and enhance the receptor-binding affinity of drugs. Anti-diabetic investigation of the synthesized compounds was performed in a zebrafish model using a fluorescently labelled glucose analog 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-d-glucose (2-NBDG) as a glucose tracker. The results indicated that the modification of berberine with carbohydrate groups could give derivatives with improved anti-diabetic activity, in particular the diglucose modified berberine derivative 1 which could dramatically promote the uptake of 2-NBDG in both zebrafish larvae and their eyes even at very low concentrations. Furthermore, the fluorescence-based anti-diabetic investigation method in zebrafish shows great potential for anti-diabetic drug screening.

Characteristics of the New Insulin-Resistant Zebrafish Model

Insulin resistance, which occurs when insulin levels are sufficiently high over a prolonged period, causing the cells to fail to respond normally to the hormone. As a system for insulin resistance and diabetes drug development, insulin-resistant rodent models have been clearly established, but there is a limitation to high-throughput drug screening. Recently, zebrafish have been identified as an excellent system for drug discovery and identification of therapeutic targets, but studies on insulin resistance models have not been extensively performed. Therefore, we aimed to make a rapid insulin-resistant zebrafish model that complements the existing rodent models. To establish this model, zebrafish were treated with 10 μM insulin for 48 h. This model showed characteristics of insulin-resistant disease such as damaged pancreatic islets. Then we confirmed the recovery of the pancreatic islets after pioglitazone treatment. In addition, it was found that insulin-resistant drugs have as significant an effect in zebrafish as in humans, and these results proved the value of the zebrafish insulin resistance model for drug selection. In addition, RNA sequencing was performed to elucidate the mechanism involved. KEGG pathway enrichment analysis of differentially expressed genes showed that insulin resistance altered gene expression due to the MAPK signaling and calcium signaling pathways. This model demonstrates the utility of the zebrafish model for drug testing and drug discovery in insulin resistance and diabetes.

Broadening the phenotypic spectrum and physiological insights related to EIF2S3 variants

Mental deficiency, epilepsy, hypogonadism, microcephaly, and obesity syndrome is a severe X-linked syndrome caused by pathogenic variants in EIF2S3. The gene encodes the γ subunit of the eukaryotic translation initiation factor-2, eIF2, essential for protein translation. A recurrent frameshift variant is described in severely affected patients while missense variants usually cause a moderate phenotype. We identified a novel missense variant (c.433A>G, p.(Met145Val)) in EIF2S3 in a mildly affected patient. Studies on zebrafish confirm the pathogenicity of this novel variant and three previously published missense variants. CRISPR/Cas9 knockout of eif2s3 in zebrafish embryos recapitulate the human microcephaly and show increased neuronal cell death. Abnormal high glucose levels were identified in mutant embryos, caused by beta cell and pancreatic progenitor deficiency, not related to apoptosis. Additional studies in patient-derived fibroblasts did not reveal apoptosis. Our results provide new insights into disease physiopathology, suggesting tissue-dependent mechanisms.

Brain-Body Control of Glucose Homeostasis-Insights From Model Organisms

Tight regulation of blood glucose is essential for long term health. Blood glucose levels are defended by the correct function of, and communication between, internal organs including the gastrointestinal tract, pancreas, liver, and brain. Critically, the brain is sensitive to acute changes in blood glucose level and can modulate peripheral processes to defend against these deviations. In this mini-review we highlight select key findings showcasing the utility, strengths, and limitations of model organisms to study brain-body interactions that sense and control blood glucose levels. First, we discuss the large platform of genetic tools available to investigators studying mice and how this field may yet reveal new modes of communication between peripheral organs and the brain. Second, we discuss how rats, by virtue of their size, have unique advantages for the study of CNS control of glucose homeostasis and note that they may more closely model some aspects of human (patho)physiology. Third, we discuss the nascent field of studying the CNS control of blood glucose in the zebrafish which permits ease of genetic modification, large-scale measurements of neural activity and live imaging in addition to high-throughput screening. Finally, we briefly discuss glucose homeostasis in drosophila, which have a distinct physiology and glucoregulatory systems to vertebrates.

Which Hyperglycemic Model of Zebrafish (Danio rerio) Suites My Type 2 Diabetes Mellitus Research? A Scoring System for Available Methods

Despite extensive studies on type 2 diabetes mellitus (T2DM), there is no definitive cure, drug, or prevention. Therefore, for developing new therapeutics, proper study models of T2DM is necessary to conduct further preclinical researches. Diabetes has been induced in animals using chemical, genetic, hormonal, antibody, viral, and surgical methods or a combination of them. Beside different approaches of diabetes induction, different animal species have been suggested. Although more than 85% of articles have proposed rat (genus Rattus) as the proper model for diabetes induction, zebrafish (Danio rerio) models of diabetes are being used more frequently in diabetes related studies. In this systematic review, we compare different aspects of available methods of inducing hyperglycemia referred as T2DM in zebrafish by utilizing a scoring system. Evaluating 26 approved models of T2DM in zebrafish, this scoring system may help researchers to compare different T2DM zebrafish models and select the best one regarding their own research theme. Eventually, glyoxalase1 (glo1-/-) knockout model of hyperglycemia achieved the highest score. In addition to assessment of hyperglycemic induction methods in zebrafish, eight most commonly proposed diabetic induction approval methods are suggested to help researchers confirm their subsequent proposed models.

Embryonic Exposure to Low Concentrations of Bisphenol A and S Altered Genes Related to Pancreatic β-Cell Development and DNA Methyltransferase in Zebrafish

Bisphenol A (BPA) and bisphenol S (BPS) are implicated in the development of metabolic disorders, such diabetes mellitus. However, the epigenetic mechanism underlying the pancreatic β-cell dysregulation for both BPA/BPS needs clarification. This exploratory study was designed to investigate whether embryonic exposure to low BPA/BPS concentrations impair early pancreatic β-cell differentiation as well as DNA methylation in its gene expression profile using an in vivo model, zebrafish. Zebrafish embryos were exposed to 0, 0.01, 0.03, 0.1, 0.3, and 1.0 µM BPA/BPS at 4-h post fertilization (hpf) until 120 hpf. BPA/BPS-induced effects on pancreatic-related genes, insulin gene, and DNA methylation-associated genes were assessed at developmental stages (24-120 hpf), while glucose level was measure at the 120 hpf. The insulin expression levels decreased at 72-120 hpf for 1.0 µM BPA, while 0.32 and 0.24-fold of insulin expression were elicited by 0.3 and 1 µM BPS respectively at 72 hpf. Significant elevation of glucose levels; 16.3% (for 1.0 µM BPA), 7.20% (for 0.3 µM BPS), and 74.09% (for 1.0 µM BPS) higher than the control groups were observed. In addition, pancreatic-related genes pdx-1, foxa2, ptfla, and isl1 were significantly interfered compared with the untreated group. Moreover, the maintenance methylation gene, dnmt1, was monotonically and significantly decreased at early stage of development following BPA exposure but remained constant for BPS treatment relative to the control group. DNMT3a and DNMT3b orthologs were distinctively altered following BPA/BPS embryonic exposure. Our data indicated that embryonic exposure to low concentration of BPA/BPS can impair the normal expressions of pancreatic-associated genes and DNA methylation pattern of selected genes in zebrafish early development.

Enhancing glucose metabolism via gluconeogenesis is therapeutic in a zebrafish model of Dravet syndrome

Energy-producing pathways are novel therapeutic targets for the treatment of neurodevelopmental disorders. Here, we focussed on correcting metabolic defects in a catastrophic paediatric epilepsy, Dravet syndrome which is caused by mutations in sodium channel NaV1.1 gene, SCN1A. We utilized a translatable zebrafish model of Dravet syndrome (scn1lab) which exhibits key characteristics of patients with Dravet syndrome and shows metabolic deficits accompanied by down-regulation of gluconeogenesis genes, pck1 and pck2. Using a metabolism-based small library screen, we identified compounds that increased gluconeogenesis via up-regulation of pck1 gene expression in scn1lab larvae. Treatment with PK11195, a pck1 activator and a translocator protein ligand, normalized dys-regulated glucose levels, metabolic deficits, translocator protein expression and significantly decreased electrographic seizures in mutant larvae. Inhibition of pck1 in wild-type larvae mimicked metabolic and behaviour defects observed in scn1lab mutants. Together, this suggests that correcting dys-regulated metabolic pathways can be therapeutic in neurodevelopmental disorders such as Dravet syndrome arising from ion channel dysfunction.

Wild-Type Zebrafish (Danio rerio) Larvae as a Vertebrate Model for Diabetes and Comorbidities: A Review

Zebrafish have become a popular alternative to higher animals in biomedical and pharmaceutical research. The development of stable mutant lines to model target specific aspects of many diseases, including diabetes, is well reported. However, these mutant lines are much more costly and challenging to maintain than wild-type zebrafish and are simply not an option for many research facilities. As an alternative to address the disadvantages of advanced mutant lines, wild-type larvae may represent a suitable option. In this review, we evaluate organ development in zebrafish larvae and discuss established methods that use wild-type zebrafish larvae up to seven days post fertilization to test for potential drug candidates for diabetes and its commonly associated conditions of oxidative stress and inflammation. This provides an up to date overview of the relevance of wild-type zebrafish larvae as a vertebrate antidiabetic model and confidence as an alternative tool for preclinical studies. We highlight the advantages and disadvantages of established methods and suggest recommendations for future developments to promote the use of zebrafish, specifically larvae, rather than higher animals in the early phase of antidiabetic drug discovery.

Crocins from Crocus sativus L. in the Management of Hyperglycemia. In Vivo Evidence from Zebrafish

Diabetes mellitus is a disease characterized by persistent high blood glucose levels and accompanied by impaired metabolic pathways. In this study, we used zebrafish to investigate the effect of crocins isolated from Crocus sativus L., on the control of glucose levels and pancreatic β-cells. Embryos were exposed to an aqueous solution of crocins and whole embryo glucose levels were measured at 48 h post-treatment. We showed that the application of crocins reduces zebrafish embryo glucose levels and enhances insulin expression. We also examined whether crocins are implicated in the metabolic pathway of gluconeogenesis. We showed that following a single application of crocins and glucose level reduction, the expression of phosphoenolpyruvate carboxykinase1 (pck1), a key gene involved in glucose metabolism, is increased. We propose a putative role for the crocins in glucose metabolism and insulin management.

Elevated 4-hydroxynonenal induces hyperglycaemia via Aldh3a1 loss in zebrafish and associates with diabetes progression in humans

Increased methylglyoxal (MG) formation is associated with diabetes and its complications. In zebrafish, knockout of the main MG detoxifying system Glyoxalase 1, led to limited MG elevation but significantly elevated aldehyde dehydrogenases (ALDH) activity and aldh3a1 expression, suggesting the compensatory role of Aldh3a1 in diabetes. To evaluate the function of Aldh3a1 in glucose homeostasis and diabetes, aldh3a1^−/− zebrafish mutants were generated using CRISPR-Cas9. Vasculature and pancreas morphology were analysed by zebrafish transgenic reporter lines. Corresponding reactive carbonyl species (RCS), glucose, transcriptome and metabolomics screenings were performed and ALDH activity was measured for further verification. Aldh3a1^−/− zebrafish larvae displayed retinal vasodilatory alterations, impaired glucose homeostasis, which can be aggravated via pdx1 silencing induced hyperglycaemia. Unexpectedly, MG was not altered, but 4-hydroxynonenal (4-HNE), another prominent lipid peroxidation RCS exhibited high affinity with Aldh3a1, was increased in aldh3a1 mutants. 4-HNE was responsible for the retinal phenotype via pancreas disruption induced hyperglycaemia and can be rescued via l-Carnosine treatment. Furthermore, in type 2 diabetic patients, serum 4-HNE was increased and correlated with disease progression. Thus, our data suggest impaired 4-HNE detoxification and elevated 4-HNE concentration as biomarkers but also the possible inducers for diabetes, from genetic susceptibility to the pathological progression.

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Aldh3a1 mutant was generated using CRISPR/Cas9 and displayed impaired glucose homeostasis.

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Elevated 4-Hydroxynonenal (4-HNE) was responsible for hyperglycaemia in aldh3a1 mutants and was rescued by Carnosine.

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Patient serum 4-HNE level was correlated with HbA1c and fasting glucose.

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Impaired 4-HNE detoxification acts as possible inducers for diabetes, from genetic susceptibility to pathological progress.

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.

Vascular Damage in Obesity and Diabetes: Highlighting Links Between Endothelial Dysfunction and Metabolic Disease in Zebrafish and Man

Endothelial dysfunction is an initial pathophysiological mechanism of vascular damage and is further recognized as an independent predictor of negative prognosis in diabetes-induced micro- and macrovascular complications. Insight into the capability of zebrafish to model metabolic disease like obesity and type II diabetes has increased and new evidence on the induction of vascular pathologies in zebrafish through metabolic disease is available. Here, we raise the question, if zebrafish can be utilized to study the initial impairments of vascular complications in metabolic disorders. In this review, we focus on the advances made to develop models of obesity and type II diabetes in zebrafish, discuss the key points and characteristics of these models, while highlighting the available information linked to the development of endothelial dysfunction in zebrafish and man. We show that larval and adult zebrafish develop metabolic dysregulation in the settings of obesity and diabetes, exhibiting pathophysiological mechanisms, which mimic the human condition. The most important genes related to endothelial dysfunction are present in zebrafish and further display similar functions as in mammals. Several suggested contributors to endothelial dysfunction found in these models, namely hyperinsulinaemia, hyperglycaemia, hyperlipidaemia and hyperleptinaemia are highlighted and the available data from zebrafish are summarised. Many underlying processes of endothelial dysfunction in obesity and diabetes are fundamentally present in zebrafish and provide ground for the assumption, that zebrafish can develop endothelial dysfunction. Conservation of basic biological mechanisms is established for zebrafish, but focused investigation on the subject is now needed as validation and particularly more research is necessary to understand the differences between zebrafish and man. The available data demonstrate the relevance of zebrafish as a model for metabolic disease and their ability to become a proponent for the investigation of vascular damage in the settings of obesity and diabetes.

Activation of Retinal Angiogenesis in Hyperglycemic pdx1 -/- Zebrafish Mutants

Progression from the initial vascular response upon hyperglycemia to a proliferative stage with neovacularizations is the hallmark of proliferative diabetic retinopathy. Here, we report on the novel diabetic pdx1 ^-/- zebrafish mutant as a model for diabetic retinopathy that lacks the transcription factor pdx1 through CRISPR-Cas9-mediated gene knockout leading to disturbed pancreatic development and hyperglycemia. Larval pdx1 ^-/- mutants prominently show vasodilation of blood vessels through increased vascular thickness in the hyaloid network as direct developmental precursor of the adult retinal vasculature in zebrafish. In adult pdx1 ^-/- mutants, impaired glucose homeostasis induces increased hyperbranching and hypersprouting with new vessel formation in the retina and aggravation of the vascular alterations from the larval to the adult stage. Both vascular aspects respond to antiangiogenic and antihyperglycemic pharmacological interventions in the larval stage and are accompanied by alterations in the nitric oxide metabolism. Thus, the pdx1 ^-/- mutant represents a novel model to study mechanisms of hyperglycemia-induced retinopathy wherein extensive proangiogenic alterations in blood vessel morphology and metabolic alterations underlie the vascular phenotype.

High-glucose/high-cholesterol diet in zebrafish evokes diabetic and affective pathogenesis: The role of peripheral and central inflammation, microglia and apoptosis

Neuroinflammation and metabolic deficits contribute to the etiology of human affective disorders, such as anxiety and depression. The zebrafish (Danio rerio) has recently emerged as a powerful new model organism in CNS disease modeling. Here, we exposed zebrafish to 2% glucose and 10% cholesterol for 19 days to experimentally induce type 2 diabetes (DM) and to assess stress responses, microglia, inflammation and apoptosis. We analyzed zebrafish anxiety-like behavior in the novel tank and light-dark box (Days 15-16) tests, as well as examined their biochemical and genomic biomarkers (Day 19). Confirming DM-like state in zebrafish, we found higher whole-body glucose, triglyceride, total cholesterol, low-density lipoprotein levels and glucagon mRNA expression, and lower high-density lipoprotein levels. DM zebrafish also showed anxiety-like behavior, elevated whole-body cortisol and cytokines IFN-γ and IL-4, as well as higher brain mRNA expression of the glucocorticoid receptor, CD11b (a microglial biomarker), pro-inflammatory cytokines IL-6 and TNF-α (but not IL-1β or anti-inflammatory cytokines IL-4 and IL-10), GFAP (an astrocytal biomarker), neurotrophin BDNF, its receptors p75 and TrkB, as well as apoptotic Bax and Caspase-3 (but not BCl-2) genes. Collectively, this supports the overlapping nature of DM-related affective pathogenesis and emphasizes the role of peripheral and central inflammation and apoptosis in DM-related affective and neuroendocrine deficits in zebrafish.

Zebrafish for Personalized Regenerative Medicine; A More Predictive Humanized Model of Endocrine Disease

Regenerative medicine is a multidisciplinary field that aims to determine different factors and develop various methods to regenerate impaired tissues, organs, and cells in the disease and impairment conditions. When treatment procedures are specified according to the individual's information, the leading role of personalized regenerative medicine will be revealed in developing more effective therapies. In this concept, endocrine disorders can be considered as potential candidates for regenerative medicine application. Diabetes mellitus as a worldwide prevalent endocrine disease causes different damages such as blood vessel damages, pancreatic damages, and impaired wound healing. Therefore, a global effort has been devoted to diabetes mellitus investigations. Hereupon, the preclinical study is a fundamental step. Up to now, several species of animals have been modeled to identify the mechanism of multiple diseases. However, more recent researches have been demonstrated that animal models with the ability of tissue regeneration are more suitable choices for regenerative medicine studies in endocrine disorders, typically diabetes mellitus. Accordingly, zebrafish has been introduced as a model that possesses the capacity to regenerate different organs and tissues. Especially, fine regeneration in zebrafish has been broadly investigated in the regenerative medicine field. In addition, zebrafish is a suitable model for studying a variety of different situations. For instance, it has been used for developmental studies because of the special characteristics of its larva. In this review, we discuss the features of zebrafish that make it a desirable animal model, the advantages of zebrafish and recent research that shows zebrafish is a promising animal model for personalized regenerative diseases. Ultimately, we conclude that as a newly introduced model, zebrafish can have a leading role in regeneration studies of endocrine diseases and provide a good perception of underlying mechanisms.

Bioconcentration and Metabolic Effects of Emerging PFOS Alternatives in Developing Zebrafish

The novel PFOS alternatives, 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzenesulfonate (OBS), are emerging in the Chinese market, but little is known about their ecological risks. In this study, zebrafish embryos were exposed to PFOS, F-53B, and OBS to evaluate their bioconcentration and acute metabolic consequences. Per- and polyfluoroalkyl substances (PFASs) accumulated in larvae in the order of F-53B > PFOS > OBS, with the bioconcentration factors ranging from 20 to 357. Exposure to F-53B and PFOS, but not OBS, increased energy expenditure, and reduced feed intake in a concentration-dependent manner and the expression of genes involved in metabolic pathways at the transcriptional and translational levels. Molecular docking revealed that the binding affinities of PFASs to glucokinase were decreased in the following order: F-53B > PFOS > OBS. Finally, the results of Point of Departure (PoD) indicate that metabolic end points at the molecular and organismal level are most sensitive to F-53B followed by PFOS and OBS. Collectively, F-53B has the highest bioconcentration potential and the strongest metabolism-disrupting effects, followed by PFOS and OBS. Our findings have important implications for the assessment of early developmental metabolic effects of PFOS alternatives F-53B and OBS in wildlife and humans.

Disruption of the pancreatic vasculature in zebrafish affects islet architecture and function

A dense local vascular network is crucial for pancreatic endocrine cells to sense metabolites and secrete hormones, and understanding the interactions between the vasculature and the islets may allow for therapeutic modulation in disease conditions. Using live imaging in two models of vascular disruption in zebrafish, we identified two distinct roles for the pancreatic vasculature. At larval stages, expression of a dominant negative version of Vegfaa (dnVegfaa) in β-cells led to vascular and endocrine cell disruption with a minor impairment in β-cell function. In contrast, expression of a soluble isoform of Vegf receptor 1 (sFlt1) in β-cells blocked the formation of the pancreatic vasculature and drastically stunted glucose response, although islet architecture was not affected. Notably, these effects of dnVegfaa or sFlt1 were not observed in animals lacking vegfaa, vegfab, kdrl, kdr or flt1 function, indicating that they interfere with multiple ligands and/or receptors. In adults, disrupted islet architecture persisted in dnVegfaa-expressing animals, whereas sFlt1-expressing animals displayed large sheets of β-cells along their pancreatic ducts, accompanied by impaired glucose tolerance in both models. Thus, our study reveals novel roles for the vasculature in patterning and function of the islet.

CNDP1 knockout in zebrafish alters the amino acid metabolism, restrains weight gain, but does not protect from diabetic complications

The gene CNDP1 was associated with the development of diabetic nephropathy. Its enzyme carnosinase 1 (CN1) primarily hydrolyzes the histidine-containing dipeptide carnosine but other organ and metabolic functions are mainly unknown. In our study we generated CNDP1 knockout zebrafish, which showed strongly decreased CN1 activity and increased intracellular carnosine levels. Vasculature and kidneys of CNDP1-/- zebrafish were not affected, except for a transient glomerular alteration. Amino acid profiling showed a decrease of certain amino acids in CNDP1-/- zebrafish, suggesting a specific function for CN1 in the amino acid metabolisms. Indeed, we identified a CN1 activity for Ala-His and Ser-His. Under diabetic conditions increased carnosine levels in CNDP1-/- embryos could not protect from respective organ alterations. Although, weight gain through overfeeding was restrained by CNDP1 loss. Together, zebrafish exhibits CN1 functions, while CNDP1 knockout alters the amino acid metabolism, attenuates weight gain but cannot protect organs from diabetic complications.

Disruption of peripheral nerve development in a zebrafish model of hyperglycemia

Diabetes mellitus-induced hyperglycemia is associated with a number of pathologies such as retinopathy, nephropathy, delayed wound healing, and diabetic peripheral neuropathy (DPN). Approximately 50% of patients with diabetes mellitus will develop DPN, which is characterized by disrupted sensory and/or motor functioning, with treatment limited to pain management. Zebrafish ( Danio rerio) are an emerging animal model used to study a number of metabolic disorders, including diabetes. Diabetic retinopathy, nephropathy, and delayed wound healing have all been demonstrated in zebrafish. Recently, our laboratory has demonstrated that following the ablation of the insulin-producing β-cells of the pancreas (and subsequent hyperglycemia), the peripheral nerves begin to show signs of dysregulation. In this study, we take a different approach, taking advantage of the transdermal absorption abilities of zebrafish larvae to extend the period of hyperglycemia. Following 5 days of 60 mM d-glucose treatment, we observed motor axon defasciculation, disturbances in perineurial glia sheath formation, decreased myelination of motor axons, and sensory neuron mislocalization. This study extends our understanding of the structural changes of the peripheral nerve following induction of hyperglycemia and does so in an animal model capable of potential DPN drug discovery in the future.

NEW & NOTEWORTHY Zebrafish are emerging as a robust model system for the study of diabetic complications such as retinopathy, nephropathy, and impaired wound healing. We present a novel model of diabetic peripheral neuropathy in zebrafish in which the integrity of the peripheral nerve is dysregulated following the induction of hyperglycemia. By using this model, future studies can focus on elucidating the underlying molecular mechanisms currently unknown.

Embryonic exposure to oxy-polycyclic aromatic hydrocarbon interfere with pancreatic β-cell development in zebrafish via altering DNA methylation and gene expression

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are a class of anthropogenic, persistent and very toxic PAH contaminant associated with developmental toxicity. Abnormal glucose metabolism disturbs energy balances that impair the early development of vertebrates, but the mechanisms by which maternal OPAH exposure alters glucose homeostasis in offspring are not well understood. Studies have suggested that epigenetic changes, particularly in DNA methylation, provide a memory of plastic developmental responses to the environment, leading to the generation of novel offspring phenotypes. The objective of this study is to test the hypothesis that embryonic exposure to low-dose OPAH can impair early β-cell differentiation in zebrafish (Danio rerio) by altering DNA methylation and gene expression. The zebrafish embryos were exposed to 0, 0.03, 0.1, 0.3, 1 and 3 μM 9‑fluorenone (9-FLO) at 3 h postfertilization (hpf) until 120 hpf to assess pancreatic organogenesis. 9-FLO exposure reduced total body length, eye length and heart rate, decreased insulin generation, interfered with glucose metabolism, and altered the expression of pancreatic organogenesis-related genes pdx-1, foxa2, isl1 and ptf1a. In particular, low-dose embryonic 9-FLO exposure significantly decreased β-cell differentiation marker gene pdx-1 mRNA levels, indicating that pancreatic endocrine is a more sensitive target response to embryonic low-dose OPAH exposure. Additionally, we found that DNA methyltransferases dnmt1 and dnmt3 were elevated and the DNA methylation at promoter regions of pdx-1 was increased at an early stage of development. These data demonstrated that the low-dose OPAH embryonic exposure can impair pancreatic endocrine development by increasing DNA methylation at the promoter regions of pdx-1 that are essential for β-cell differentiation.

Acute effects of hyperglycemia on the peripheral nervous system in zebrafish (Danio rerio) following nitroreductase-mediated β-cell ablation

Diabetic peripheral neuropathy (DPN) is estimated to affect 50% of diabetic patients. Although DPN is highly prevalent, molecular mechanisms remain unknown and treatment is limited to pain relief and glycemic control. We provide a novel model of acute DPN in zebrafish ( Danio rerio) larvae. Beginning 5 days postfertilization (dpf), zebrafish expressing nitroreductase in their pancreatic β-cells were treated with metronidazole (MTZ) for 48 h and checked for β-cell ablation 7 dpf. In experimental design, this was meant to serve as proof of concept that β-cell ablation and hyperglycemia are possible at this time point, but we were surprised to find changes in both sensory and motor nerve components. Compared with controls, neurod+ sensory neurons were often observed outside the dorsal root ganglia in MTZ-treated fish. Fewer motor nerves were properly ensheathed by nkx2.2a+ perineurial cells, and tight junctions were disrupted along the motor nerve in MTZ-treated fish compared with controls. Not surprisingly, the motor axons of the MTZ-treated group were defasciculated compared with the control group, myelination was attenuated, and there was a subtle difference in Schwann cell number between the MTZ-treated and control group. All structural changes occurred in the absence of behavioral changes in the larvae at this time point, suggesting that peripheral nerves are influenced by acute hyperglycemia before becoming symptomatic. Moving forward, this novel animal model of DPN will allow us to access the molecular mechanisms associated with the acute changes in the hyperglycemic peripheral nervous system, which may help direct therapeutic approaches.

Sweet fish: Fish models for the study of hyperglycemia and diabetes

Fish are good for your health in more ways than you may expect. For one, eating fish is a common dietary recommendation for a healthy diet. However, fish have much more to provide than omega-3 fatty acids to your circulatory system. Some fish species now serve as important and innovative model systems for diabetes research, providing novel and unique advantages compared with classical research models. Not surprisingly, the largest share of diabetes research in fish occurs in the laboratory workhorse among fish, the zebrafish (Danio rerio). Established as a genetic model system to study development, these small cyprinid fish have eventually conquered almost every scientific discipline and, over the past decade, have emerged as an important model system for metabolic diseases, including diabetes mellitus. In this review we highlight the practicability of using zebrafish to study diabetes and hyperglycemia, and summarize some of the recent research and breakthroughs made using this model. Equally exciting is the appearance of another emerging discipline, one that is taking advantage of evolution by studying cases of naturally occurring insulin resistance in fish species. We briefly discuss two such models in this review, namely the rainbow trout (Oncorhynchus mykiss) and the cavefish (Astyanax mexicanus).

In vivo imaging of β-cell function reveals glucose-mediated heterogeneity of β-cell functional development

How pancreatic β-cells acquire function in vivo is a long-standing mystery due to the lack of technology to visualize β-cell function in living animals. Here, we applied a high-resolution two-photon light-sheet microscope for the first in vivo imaging of Ca²⁺activity of every β-cell in Tg (ins:Rcamp1.07) zebrafish. We reveal that the heterogeneity of β-cell functional development in vivo occurred as two waves propagating from the islet mantle to the core, coordinated by islet vascularization. Increasing amounts of glucose induced functional acquisition and enhancement of β-cells via activating calcineurin/nuclear factor of activated T-cells (NFAT) signaling. Conserved in mammalians, calcineurin/NFAT prompted high-glucose-stimulated insulin secretion of neonatal mouse islets cultured in vitro. However, the reduction in low-glucose-stimulated insulin secretion was dependent on optimal glucose but independent of calcineurin/NFAT. Thus, combination of optimal glucose and calcineurin activation represents a previously unexplored strategy for promoting functional maturation of stem cell-derived β-like cells in vitro.

When the amount of sugar in our body rises, specialised cells known as β-cells respond by releasing insulin, a hormone that acts on various organs to keep blood sugar levels within a healthy range. These cells cluster in small ‘islets’ inside our pancreas. If the number of working β-cells declines, diseases such as diabetes may appear and it becomes difficult to regulate the amount of sugar in our bodies. Understanding how β-cells normally develop and mature in the embryo could help us learn how to make new ones in the laboratory. In particular, researchers are interested in studying how different body signals, such as blood sugar levels, turn immature β-cells into fully productive cells. However, in mammals, the pancreas and its islets are buried deep inside the embryo and they cannot be observed easily.

Here, Zhao et al. circumvented this problem by doing experiments on zebrafish embryos, which are transparent, grow outside their mother’s body, and have pancreatic islets that are similar to the ones found in mammals. A three-dimensional microscopy technique was used to watch individual β-cells activity over long periods, which revealed that the cells start being able to produce insulin at different times. The β-cells around the edge of each islet were the first to have access to blood sugar signals: they gained their hormone-producing role earlier than the cells in the core of an islet, which only sensed the information later on.

Zhao et al. then exposed the zebrafish embryos to different amounts of sugar. This showed that there is an optimal concentration of sugar which helps β-cells develop by kick-starting a cascade of events inside the cell. Further experiments confirmed that the same pathway and optimal sugar concentration exist for mammalian islets grown in the laboratory.

These findings may help researchers find better ways of making new β-cells to treat diabetic patients. In the future, using the three-dimensional imaging technique in zebrafish embryos may lead to more discoveries on how the pancreas matures.

Impairment of bisphenol F on the glucose metabolism of zebrafish larvae

Bisphenol F (BPF) is a substitute of bisphenol A in the production of epoxy resin and polycarbonate. Its extensive use in consumer products leads to a wide human exposure at high levels. Although the adverse effects of BPF on animal health are of increasing public concern, its risks on systematic glucose metabolism and blood glucose concentrations still remain largely unknown. Using zebrafish larvae as the model animal, we investigated the disturbance of BPF exposure on glucose metabolism and the underlying mechanisms. Zebrafish larvae at 96 h post fertilization were exposed to 0.1, 1, 10, and 100 μg/L of BPF for 48 h. Compared with the control group, glucose levels of larvae increased significantly in the 10 and 100 μg/L exposure groups, which are associated with enhancement of gluconeogenesis and suppression of glycolysis induced by high doses of BPF. Additionally, both mRNA expressions and protein levels of insulin increased significantly in the 10 and 100 μg/L exposure groups, while transcription levels of genes encoding insulin receptor substrates decreased significantly in these groups, indicating a possibly decreased insulin sensitivity due to impairment of insulin signaling transduction downstream of insulin receptor. Further, compared with BPF alone, co-exposure of larvae to BPF and rosiglitazone, an insulin sensitizer, significantly attenuates increases in both glucose levels and mRNA expressions of a key gluconeogenesis enzyme. Our data therefore indicate impairing insulin signaling transduction may be the main mechanism through which BPF disrupts glucose metabolism and induces hyperglycemia. Results of the present study inform the health risk assessment of BPF and also suggest the use of zebrafish larvae in large-scale screening of chemicals with possible glucose metabolism disturbing effect.

Screening for insulin-independent pathways that modulate glucose homeostasis identifies androgen receptor antagonists

Pathways modulating glucose homeostasis independently of insulin would open new avenues to combat insulin resistance and diabetes. Here, we report the establishment, characterization, and use of a vertebrate ‘insulin-free’ model to identify insulin-independent modulators of glucose metabolism. insulin knockout zebrafish recapitulate core characteristics of diabetes and survive only up to larval stages. Utilizing a highly efficient endoderm transplant technique, we generated viable chimeric adults that provide the large numbers of insulin mutant larvae required for our screening platform. Using glucose as a disease-relevant readout, we screened 2233 molecules and identified three that consistently reduced glucose levels in insulin mutants. Most significantly, we uncovered an insulin-independent beneficial role for androgen receptor antagonism in hyperglycemia, mostly by reducing fasting glucose levels. Our study proposes therapeutic roles for androgen signaling in diabetes and, more broadly, offers a novel in vivo model for rapid screening and decoupling of insulin-dependent and -independent mechanisms.

Diabetes is a disease that affects the ability of the body to control the level of sugar in the blood. Individuals with diabetes are unable to make a hormone called insulin – which normally stimulates certain cells to absorb sugar from the blood – or their cells are less able to respond to this hormone. Most treatments for diabetes involve replacing the lost insulin or boosting the hormone’s activity in the body. However, these treatments can also cause individuals to gain weight or become more resistant to insulin, making it harder to control blood sugar levels.

In addition to insulin, several other factors regulate the levels of sugar in the blood and some of them may operate independently of insulin. However, little is known about such factors because it is impractical to carry out large-scale screens to identify drugs that target them in humans or mice, which are often used as experimental models for human biology.

To overcome this challenge, Mullapudi et al. turned to another animal known as the zebrafish and generated mutant fish that lack insulin. The mutant zebrafish had similar problems with regulating sugar levels as those observed in humans and mice with diabetes. This observation suggests that insulin is just as important in zebrafish as it is in humans and other mammals.

The mutant zebrafish did not survive into adulthood, and so Mullapudi et al. transplanted healthy tissue into the zebrafish to allow them to produce enough insulin to survive. These adult zebrafish produced many offspring that still carried the insulin mutation. Mullapudi et al. used these mutant offspring to screen over 2,000 drugs for their ability to decrease blood sugar levels in the absence of insulin. The screen identified three promising candidate drugs, including a molecule that interferes with a receptor for a signal known as androgen.

These findings will help researchers investigate new ways to treat diabetes. In the future, the screening approach developed by Mullapudi et al. could be adapted to search for new drugs to treat other human metabolic conditions.

Loss of the Mia40a oxidoreductase leads to hepato-pancreatic insufficiency in zebrafish

Development and function of tissues and organs are powered by the activity of mitochondria. In humans, inherited genetic mutations that lead to progressive mitochondrial pathology often manifest during infancy and can lead to death, reflecting the indispensable nature of mitochondrial biogenesis and function. Here, we describe a zebrafish mutant for the gene mia40a (chchd4a), the life-essential homologue of the evolutionarily conserved Mia40 oxidoreductase which drives the biogenesis of cysteine-rich mitochondrial proteins. We report that mia40a mutant animals undergo progressive cellular respiration defects and develop enlarged mitochondria in skeletal muscles before their ultimate death at the larval stage. We generated a deep transcriptomic and proteomic resource that allowed us to identify abnormalities in the development and physiology of endodermal organs, in particular the liver and pancreas. We identify the acinar cells of the exocrine pancreas to be severely affected by mutations in the MIA pathway. Our data contribute to a better understanding of the molecular, cellular and organismal effects of mitochondrial deficiency, important for the accurate diagnosis and future treatment strategies of mitochondrial diseases.

Mitochondrial pathologies which result from mutations in the nuclear DNA remain incurable and often lead to death. As mitochondria play various roles in cellular and tissue-specific contexts, the symptoms of mitochondrial pathologies can differ between patients. Thus, diagnosis and treatment of mitochondrial disorders remain challenging. To enhance this, the generation of new models that explore and define the consequences of mitochondria insufficiencies is of central importance. Here, we present a mia40a zebrafish mutant as a model for mitochondrial dysfunction, caused by an imbalance in mitochondrial protein biogenesis. This mutant shares characteristics with existing reports on mitochondria dysfunction, and has led us to identify novel phenotypes such as enlarged mitochondrial clusters in skeletal muscles. In addition, our transcriptomics and proteomics data contribute important findings to the existing knowledge on how faulty mitochondria impinge on vertebrate development in molecular, tissue and organ specific contexts.

Zebrafish as a Model for Obesity and Diabetes

Obesity and diabetes now considered global epidemics. The prevalence rates of diabetes are increasing in parallel with the rates of obesity and the strong connection between these two diseases has been coined as “diabesity.” The health risks of overweight or obesity include Type 2 diabetes mellitus (T2DM), coronary heart disease and cancer of numerous organs. Both obesity and diabetes are complex diseases that involve the interaction of genetics and environmental factors. The underlying pathogenesis of obesity and diabetes are not well understood and further research is needed for pharmacological and surgical management. Consequently, the use of animal models of obesity and/or diabetes is important for both improving the understanding of these diseases and to identify and develop effective treatments. Zebrafish is an attractive model system for studying metabolic diseases because of the functional conservation in lipid metabolism, adipose biology, pancreas structure, and glucose homeostasis. It is also suited for identification of novel targets associated with the risk and treatment of obesity and diabetes in humans. In this review, we highlight studies using zebrafish to model metabolic diseases, and discuss the advantages and disadvantages of studying pathologies associated with obesity and diabetes in zebrafish.

In vivo monitoring of intracellular Ca2+ dynamics in the pancreatic β-cells of zebrafish embryos

Assessing the response of pancreatic islet cells to glucose stimulation is important for understanding β-cell function. Zebrafish are a promising model for studies of metabolism in general, including stimulus-secretion coupling in the pancreas. We used transgenic zebrafish embryos expressing a genetically-encoded Ca²⁺ sensor in pancreatic β-cells to monitor a key step in glucose induced insulin secretion; the elevations of intracellular [Ca²⁺]_i. In vivo and ex vivo analyses of [Ca²⁺]_i demonstrate that β-cell responsiveness to glucose is well established in late embryogenesis and that embryonic β-cells also respond to free fatty acid and amino acid challenges. In vivo imaging of whole embryos further shows that indirect glucose administration, for example by yolk injection, results in a slow and asynchronous induction of β-cell [Ca²⁺]_i responses, while intravenous glucose injections cause immediate and islet-wide synchronized [Ca²⁺]_i fluctuations. Finally, we demonstrate that embryos with disrupted mutation of the Ca_V1.2 channel gene cacna1c are hyperglycemic and that this phenotype is associated with glucose-independent [Ca²⁺]_i fluctuation in β-cells. The data reveal a novel central role of cacna1c in β-cell specific stimulus-secretion coupling in zebrafish and demonstrate that the novel approach we propose - to monitor the [Ca²⁺]_i dynamics in embryonic β-cells in vivo - will help to expand the understanding of β-cell physiological functions in healthy and diseased states.