Modeling hypercholesterolemia and vascular lipid accumulation in LDL receptor mutant zebrafish

6-PPD triggered lipid metabolism disorder and inflammatory response in larval zebrafish (Danio rerio) by regulating PPARγ/NF-κB pathway

As a synthetic rubber antioxidant, the environmental monitoring concentrations of N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD) have exceeded the risk threshold, attracting widespread attention. Although investigations into the harmful effects on zebrafish have commenced, a comprehensive exploration of its toxicological impacts and underlying molecular mechanisms remains to be conducted. By using zebrafish as a model, this study systematically evaluated 6-PPD-induced lipid metabolism disorders and inflammation response following environmental exposure. Bioinformatics analysis revealed that 6-PPD target genes enriched in the hepatitis B pathway, indicating potential hepatic toxicity via inflammatory pathways. Therefore, we hypothesize that 6-PPD could trigger hepatotoxicity through the crosstalk between lipid metabolism and inflammation. Further experiments substantiated this hypothesis by showing lipid accumulation in the liver following 6-PPD exposure, along with elevated triglyceride (TG) and total cholesterol (TC) levels, and imbalanced expression of lipid metabolism-related marker genes. Additionally, 6-PPD exposure induced the accumulation of reactive oxygen species (ROS) and inhibited the differentiation and maturation of immune cells, resulting in immune evasion. Most of these abnormalities were exacerbated in a dose-dependent manner with increasing concentrations of 6-PPD. The addition of the PPARγ pathway agonist puerarin (PUE) or NF-κB pathway inhibitor quinazoline (QNZ) to 6-PPD exposure group mitigated these toxic effects, validating our conjecture that lipid metabolism disorder and inflammatory responses may result from the regulation of the PPARγ/NF-κB pathway.

Effect of Dietary Cholesterol, Phytosterol, and Docosahexaenoic Acid on Astaxanthin Absorption and Retention in Rainbow Trout

Astaxanthin (Ax) determines the flesh redness of a salmonid fish which is the most desirable quality indicator by consumers. Fish cannot synthesize Ax de novo, therefore, the only way to increase flesh redness is to increase dietary input or improve the absorption and retention rate of dietary Ax. As a hydrophobic carotenoid, the absorption of Ax can be modulated by other lipid molecules in the diet. The present study explored the effect of three lipids, cholesterol (CH), phytosterol (PS), and docosahexaenoic acid (DHA) on Ax absorption, transport, and retention in rainbow trout. Dietary CH significantly improved Ax absorption by elevating plasma Ax levels (p < 0.05); however, it had no effect on the whole body Ax or flesh color. Dietary PS appears to inhibit Ax absorption since fish had significantly (p < 0.05) reduced whole body Ax. Dietary DHA appeared to have no effect on Ax absorption or retention. By comparing intestinal transcriptomes, a low density lipoprotein receptor (ldlr) gene was significantly downregulated in fish fed the CH diet as compared to the control diet. Since LDLR protein plays a major role in plasma lipoprotein turnover, we hypothesized that the inhibition of ldlr gene by high dietary CH resulted in higher retention of plasma Ax. The elevation of plasma Ax was not reflected in higher flesh coloration, which suggested other limiting factors governing Ax retention in the muscle. On the other hand, the transcriptomic and proteomic analyses found no changes of genes or proteins involved in Ax absorption, transport, or excretion in fish fed PS or DHA diets as compared to the control diet. In conclusion, this study has suggested that CH promotes Ax absorption by regulating lipoprotein retention and provide evidence for improving Ax absorption via dietary modulation.

Deconvolving Passive and Active Targeting of Liposomes Bearing LDL Receptor Binding Peptides Using the Zebrafish Embryo Model

Improving target versus off-target ratio in nanomedicine remains a major challenge for increasing drug bioavailability and reducing toxicity. Active targeting using ligands on nanoparticle surfaces is a key approach but has limited clinical success. A potential issue is the integration of targeting ligands also changes the physicochemical properties of nanoparticles (passive targeting). Direct studies to understand the mechanisms of active targeting and off-targeting in vivo are limited by the lack of suitable tools. Here, the biodistribution of a representative active targeting liposome is analyzed, modified with an apolipoprotein E (ApoE) peptide that binds to the low-density lipoprotein receptor (LDLR), using zebrafish embryos. The ApoE liposomes demonstrated the expected liver targeting effect but also accumulated in the kidney glomerulus. The ldlra-/- zebrafish is developed to explore the LDLR-specificity of ApoE liposomes. Interestingly, liver targeting depends on the LDLR-specific interaction, while glomerular accumulation is independent of LDLR and peptide sequence. It is found that cationic charges of peptides and the size of liposomes govern glomerular targeting. Increasing the size of ApoE liposomes can avoid this off-targeting. Taken together, the study shows the potential of the zebrafish embryo model for understanding active and passive targeting mechanisms, that can be used to optimize the design of nanoparticles.

Directly Measuring Atherogenic Lipoprotein Kinetics in Zebrafish with the Photoconvertible LipoTimer Reporter

Lipoprotein kinetics are a crucial factor in understanding lipoprotein metabolism since a prolonged time in circulation can contribute to the atherogenic character of apolipoprotein-B (ApoB)-containing lipoproteins (B-lps). Here, we report a method to directly measure lipoprotein kinetics in live developing animals. We developed a zebrafish geneticly encoded reporter, LipoTimer, in which endogenous ApoBb.1 is fused to the photoconvertible fluorophore Dendra2 which shift its emission profile from green to red upon UV exposure. By quantifying the red population of ApoB-Dendra2 over time, we found that B-lp turnover in wild-type larvae becomes faster as development proceeds. Mutants with impaired B-lp uptake or lipolysis present with increased B-lp levels and half-life. In contrast, mutants with impaired B-lp triglyceride loading display slightly fewer and smaller-B-lps, which have a significantly shorter B-lp half-life. Further, we showed that chronic high-cholesterol feeding is associated with a longer B-lp half-life in wild-type juveniles but does not lead to changes in B-lp half-life in lipolysis deficient apoC2 mutants. These data support the hypothesis that B-lp lipolysis is suppressed by the flood of intestinal-derived B-lps that follow a high-fat meal.

Zebrafish ApoB-Containing Lipoprotein Metabolism: A Closer Look

Zebrafish have become a powerful model of mammalian lipoprotein metabolism and lipid cell biology. Most key proteins involved in lipid metabolism, including cholesteryl ester transfer protein, are conserved in zebrafish. Consequently, zebrafish exhibit a human-like lipoprotein profile. Zebrafish with mutations in genes linked to human metabolic diseases often mimic the human phenotype. Zebrafish larvae develop rapidly and externally around the maternally deposited yolk. Recent work revealed that any disturbance of lipoprotein formation leads to the accumulation of cytoplasmic lipid droplets and an opaque yolk, providing a visible phenotype to investigate disturbances of the lipoprotein pathway, already leading to discoveries in MTTP (microsomal triglyceride transfer protein) and ApoB (apolipoprotein B). By 5 days of development, the digestive system is functional, making it possible to study fluorescently labeled lipid uptake in the transparent larvae. These and other approaches enabled the first in vivo description of the STAB (stabilin) receptors, showing lipoprotein uptake in endothelial cells. Various zebrafish models have been developed to mimic human diseases by mutating genes known to influence lipoproteins (eg, ldlra, apoC2). This review aims to discuss the most recent research in the zebrafish ApoB-containing lipoprotein and lipid metabolism field. We also summarize new insights into lipid processing within the yolk cell and how changes in lipid flux alter yolk opacity. This curious new finding, coupled with the development of several techniques, can be deployed to identify new players in lipoprotein research directly relevant to human disease.

Lipid regulation of protocatechualdehyde and hydroxysafflor yellow A via AMPK/SREBP2/PCSK9/LDLR signaling pathway in hyperlipidemic zebrafish

The consumption of a high-cholesterol diet is known to cause hyperlipidemia, which is one of the main risk factors for cardiovascular disease. Protocatechualdehyde (PCA) and hydroxysafflor yellow A (HSYA) are the active components of Salvia miltiorrhiza and safflower, respectively. However, their exact mechanism is still unclear. The aim of this study is to investigate its effects on lipid deposition and liver damage in hyperlipidemic zebrafish and its mechanism of anti-hyperlipidemia. The results showed that the use of PCA and HSYA alone and in combination can improve lipid deposition, slow behavior, abnormal blood flow and liver tissue damage, and the combined use is more effective. Further RT-qPCR results showed that PCA + HSYA can regulate the mRNA levels of PPAR-γ, SREBP2, SREBP1, HMGCR, PCSK9, mTOR, C/EBPα, LDLR, AMPK, HNF-1α and FoxO3a. The PCA + HSYA significantly improves lipid deposition and abnormal liver function in hyperlipidemic zebrafish larvae, which may be related to the AMPK/SREBP2/PCSK9/LDLR signaling pathway.

Gonadal sex vs genetic sex in experimental atherosclerosis

Epidemiological data and interventional studies with hormone replacement therapy suggest that women, at least until menopause, are at decreased cardiovascular risk compared to men. Still the molecular mechanisms beyond this difference are debated and the investigation in experimental models of atherosclerosis has been pivotal to prove that the activation of the estrogen receptor is atheroprotective, despite not enough to explain the differences reported in cardiovascular disease between male and female. This casts also for investigating the importance of the sex chromosome complement (genetic sex) beyond the contribution of sex hormones (gonadal sex) on atherosclerosis. Aim of this review is to present the dualism between gonadal sex and genetic sex with a focus on the data available from experimental models. The molecular mechanisms driving changes in lipid metabolism, immuno-inflammatory reactivity and vascular response in males and females that affect atherosclerosis progression will be discussed.

Zebrafish Model Insights into Mediterranean Diet Liquids: Olive Oil and Wine

In this review, we explored the potential of a zebrafish model to investigate the antioxidant effects of key components of the Mediterranean diet, namely, olive oil and wine, in the context of preventing age-related diseases, particularly cardiovascular conditions. This paper explores the spectrum of observational studies to preclinical investigations and ultimately converges toward potential translational insights derived from animal experimentation. This review highlights the potential and underutilization of zebrafish as an experimental model in this domain. We highlighted the genetic proximity of zebrafish to humans, offering a unique opportunity for translational insights into the health benefits of olive oil and wine. Indeed, we wanted to focus on the potential of zebrafish to elucidate the health benefits of olive oil and wine while calling for continued exploration to unlock its full potential to advance our knowledge of age-related disease prevention within the Mediterranean diet framework.

Exposure to PFOA and its novel analogs disrupts lipid metabolism in zebrafish

Perfluorooctanoic acid (PFOA), a typical perfluoroalkyl group compound, has received worldwide attention due to its significant environmental toxicity. Following regulatory bans on the production and emission of PFOA, concerns have been raised about the potential health risks and the safety of novel perfluoroalkyl analogues. HFPO-DA (trade name Gen-X) and HFPO-TA are two perfluoroalkyl analogues known to be bioaccumulative, whose level of toxicity and whether they are safe alternatives to PFOA remain unclear. In the following study, the physiological and metabolic effects of exposure to PFOA and its novel analogues were explored in zebrafish using 1/3 LC₅₀ (PFOA 100 μM, Gen-X 200 μM, HFPO-TA 30 μM). At the same LC₅₀ toxicological effect, exposure to PFOA and HFPO-TA resulted in abnormal phenotypes such as spinal curvature, pericardial edema and aberrant body length, while Gen-X was little changed. Metabolically, PFOA, HFPO-TA and Gen-X all significantly increased total cholesterol in exposed zebrafish with PFOA and HFPO-TA also increasing total triglyceride levels. Transcriptome analysis showed that the number of differentially expressed genes in PFOA, Gen-X, and HFPO-TA treated conditions compared to control groups were 527, 572, and 3, 933, respectively. KEGG and GO analysis of differentially expressed genes revealed pathways and functions related to lipid metabolism as well as significant activation of the peroxisome proliferators-activated receptor (PPARs) pathway. Furthermore, RT-qPCR analysis identified significant dysregulation in the downstream target genes of PPARα, which is responsible for lipid oxidative catabolism, and the SREBP pathway, which is responsible for lipid synthesis. In conclusion, both perfluoroalkyl analogues HFPO-TA and Gen-X exhibit significant physiological and metabolic toxicity to aquatic organisms and their environmental accumulation should be closely regulated.

Zebrafish as a Model of Cardiac Pathology and Toxicity: Spotlight on Uremic Toxins

Chronic kidney disease (CKD) is an increasing health care problem. About 10% of the general population is affected by CKD, representing the sixth cause of death in the world. Cardiovascular events are the main mortality cause in CKD, with a cardiovascular risk 10 times higher in these patients than the rate observed in healthy subjects. The gradual decline of the kidney leads to the accumulation of uremic solutes with a negative effect on every organ, especially on the cardiovascular system. Mammalian models, sharing structural and functional similarities with humans, have been widely used to study cardiovascular disease mechanisms and test new therapies, but many of them are rather expensive and difficult to manipulate. Over the last few decades, zebrafish has become a powerful non-mammalian model to study alterations associated with human disease. The high conservation of gene function, low cost, small size, rapid growth, and easiness of genetic manipulation are just some of the features of this experimental model. More specifically, embryonic cardiac development and physiological responses to exposure to numerous toxin substances are similar to those observed in mammals, making zebrafish an ideal model to study cardiac development, toxicity, and cardiovascular disease.

Translating atherosclerosis research from bench to bedside: navigating the barriers for effective preclinical drug discovery

Cardiovascular disease (CVD) remains the leading cause of death worldwide. An ongoing challenge remains the development of novel pharmacotherapies to treat CVD, particularly atherosclerosis. Effective mechanism-informed development and translation of new drugs requires a deep understanding of the known and currently unknown biological mechanisms underpinning atherosclerosis, accompanied by optimization of traditional drug discovery approaches. Current animal models do not precisely recapitulate the pathobiology underpinning human CVD. Accordingly, a fundamental limitation in early-stage drug discovery has been the lack of consensus regarding an appropriate experimental in vivo model that can mimic human atherosclerosis. However, when coupled with a clear understanding of the specific advantages and limitations of the model employed, preclinical animal models remain a crucial component for evaluating pharmacological interventions. Within this perspective, we will provide an overview of the mechanisms and modalities of atherosclerotic drugs, including those in the preclinical and early clinical development stage. Additionally, we highlight recent preclinical models that have improved our understanding of atherosclerosis and associated clinical consequences and propose model adaptations to facilitate the development of new and effective treatments.

Establishment of a lipid metabolism disorder model in ApoEb mutant zebrafish

BACKGROUND AND AIMS

ApoEb is a zebrafish homologous to mammalian ApoE, whose deficiency would lead to lipid metabolism disorders (LMDs) like atherosclerosis. We attempted to knock out the zebrafish ApoEb, then establish a zebrafish model with LMD.

METHODS

ApoEb was knocked out using the CRISPR/Cas9 system, and the accumulation of lipids was confirmed by Oil Red O staining, confocal imaging, and lipid measurements. The lipid-lowering effects of simvastatin (SIM), ezetimibe (EZE) and Xuezhikang (XZK), an extract derived from red yeast rice, were evaluated through in vivo imaging in zebrafish larvae.

RESULTS

In the ApoEb mutant, significant vascular lipid deposition occurred, and lipid measurement performed in the whole-body homogenate of larvae and adult plasma showed significantly increased lipid levels. SIM, EZE and XZK apparently relieved hyperlipidemia in ApoEb mutants, and XZK had a significant inhibitory effect on the recruitment of neutrophils and macrophages.

CONCLUSIONS

In this study, an LMD model has been established in ApoEb mutant zebrafish. We suggest that this versatile model could be applied in studying hypercholesterolemia and related vascular pathology in the context of early atherosclerosis, as well as the physiological function of ApoE.

Non-Mouse Models of Atherosclerosis: Approaches to Exploring the Translational Potential of New Therapies

Cardiovascular disease is the largest single cause of disease-related mortality worldwide and the major underlying pathology is atherosclerosis. Atherosclerosis develops as a complex process of vascular lipid deposition and retention by modified proteoglycans, endothelial dysfunction and unresolved chronic inflammation. There are a multitude of current therapeutic agents, most based on lowering plasma lipid levels, but, overall, they have a lower than optimum level of efficacy and many deaths continue to arise from cardiovascular disease world-wide. To identify and evaluate potential novel cardiovascular drugs, suitable animal models that reproduce human atherosclerosis with a high degree of fidelity are required as essential pre-clinical research tools. Commonly used animal models of atherosclerosis include mice (ApoE-/-, LDLR-/- mice and others), rabbits (WHHL rabbits and others), rats, pigs, hamster, zebrafish and non-human primates. Models based on various wild-type and genetically modified mice have been extensively reviewed but mice may not always be appropriate. Thus, here, we provide an overview of the advantages and shortcomings of various non-mouse animal models of atherosclerotic plaque formation, and plaque rupture, as well as commonly used interventional strategies. Taken together, the combinatorial selection of suitable animal models readily facilitates reproducible and rigorous translational research in discovering and validating novel anti-atherosclerotic drugs.

Cold shock domain-containing protein E1 is a posttranscriptional regulator of the LDL receptor

The low-density lipoprotein receptor (LDLR) controls cellular delivery of cholesterol and clears LDL from the bloodstream, protecting against atherosclerotic heart disease, the leading cause of death in the United States. We therefore sought to identify regulators of the LDLR beyond the targets of current therapies and known causes of familial hypercholesterolemia. We found that cold shock domain-containing protein E1 (CSDE1) enhanced hepatic LDLR messenger RNA (mRNA) decay via its 3' untranslated region and regulated atherogenic lipoproteins in vivo. Using parallel phenotypic genome-wide CRISPR interference screens in a tissue culture model, we identified 40 specific regulators of the LDLR that were not previously identified by observational human genetic studies. Among these, we demonstrated that, in HepG2 cells, CSDE1 regulated the LDLR at least as strongly as statins and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors. In addition, we showed that hepatic gene silencing of Csde1 treated diet-induced dyslipidemia in mice to a similar degree as Pcsk9 silencing. These results suggest the therapeutic potential of targeting CSDE1 to manipulate the posttranscriptional regulation of the LDLR mRNA for the prevention of cardiovascular disease. Our approach of modeling a clinically relevant phenotype in a forward genetic screen, followed by mechanistic pharmacologic dissection and in vivo validation, may serve as a generalizable template for the identification of therapeutic targets in other human disease states.

Novel mRNA therapy restores GALT protein and enzyme activity in a zebrafish model of classic galactosemia

Messenger RNA (mRNA) has emerged as a novel therapeutic approach for inborn errors of metabolism. Classic galactosemia (CG) is an inborn error of galactose metabolism caused by a severe deficiency of galactose-1-phosphate:uridylyltransferase (GALT) activity leading to neonatal illness and chronic impairments affecting the brain and female gonads. In this proof of concept study, we used our zebrafish model for CG to evaluate the potential of human GALT mRNA (hGALT mRNA) packaged in two different lipid nanoparticles to restore GALT expression and activity at early stages of development. Both one cell-stage and intravenous single-dose injections resulted in hGALT protein expression and enzyme activity in the CG zebrafish (galt knockout) at 5 days post fertilization (dpf). Moreover, the levels of galactose-1-phosphate (Gal-1-P) and galactonate, metabolites that accumulate because of the deficiency, showed a decreasing trend. LNP-packaged mRNA was effectively translated and processed in the CG zebrafish without signs of toxicity. This study shows that mRNA therapy restores GALT protein and enzyme activity in the CG zebrafish model, and that the zebrafish is a suitable system to test this approach. Further studies are warranted to assess whether repeated injections safely mitigate the chronic impairments of this disease.

Animal Models of Atherosclerosis-Supportive Notes and Tricks of the Trade

Atherosclerotic cardiovascular disease is a major cause of death among humans. Animal models have shown that cholesterol and inflammation are causatively involved in the disease process. Apolipoprotein B-containing lipoproteins elicit immune reactions and instigate inflammation in the vessel wall. Still, a treatment that is specific to vascular inflammation is lacking, which motivates continued in vivo investigations of the immune-vascular interactions that drive the disease. In this review, we distill old notions with emerging concepts into a contemporary understanding of vascular disease models. Pros and cons of different models are listed and the complex integrative interplay between cholesterol homeostasis, immune activation, and adaptations of the vascular system is discussed. Key limitations with atherosclerosis models are highlighted, and we suggest improvements that could accelerate progress in the field. However, excessively rigid experimental guidelines or limiting usage to certain animal models can be counterproductive. Continued work in improved models, as well as the development of new models, should be of great value in research and could aid the development of cardiovascular disease diagnostics and therapeutics of the future.

Anionic Lipid Nanoparticles Preferentially Deliver mRNA to the Hepatic Reticuloendothelial System

Lipid nanoparticles (LNPs) are the leading nonviral technologies for the delivery of exogenous RNA to target cells in vivo. As systemic delivery platforms, these technologies are exemplified by Onpattro, an approved LNP-based RNA interference therapy, administered intravenously and targeted to parenchymal liver cells. The discovery of systemically administered LNP technologies capable of preferential RNA delivery beyond hepatocytes has, however, proven more challenging. Here, preceded by comprehensive mechanistic understanding of in vivo nanoparticle biodistribution and bodily clearance, an LNP-based messenger RNA (mRNA) delivery platform is rationally designed to preferentially target the hepatic reticuloendothelial system (RES). Evaluated in embryonic zebrafish, validated in mice, and directly compared to LNP-mRNA systems based on the lipid composition of Onpattro, RES-targeted LNPs significantly enhance mRNA expression both globally within the liver and specifically within hepatic RES cell types. Hepatic RES targeting requires just a single lipid change within the formulation of Onpattro to switch LNP surface charge from neutral to anionic. This technology not only provides new opportunities to treat liver-specific and systemic diseases in which RES cell types play a key role but, more importantly, exemplifies that rational design of advanced RNA therapies must be preceded by a robust understanding of the dominant nano-biointeractions involved.

The zebrafish model system for dyslipidemia and atherosclerosis research: Focus on environmental/exposome factors and genetic mechanisms

Dyslipidemias and atherosclerosis play a pivotal role in cardiovascular risk and disease. Although some pathophysiological mechanisms underlying these conditions have been unveiled, several knowledge gaps still remain. Experimental models, both in vitro and in vivo, have been instrumental to our better understanding of such complex processes. The latter have often been based on rodent species, either wild-type or, in several instances, genetically modified. In this context, the zebrafish may represent an additional very useful in vivo experimental model for dyslipidemia and atherosclerosis. Interestingly, the lipid metabolism of zebrafish shares several features with that present in humans, recapitulating some molecular features and pathophysiological aspects in a better way than that of rodents. The zebrafish model may be of help to address questions related to exposome factors as well as to genetic features, aiming to dissect selected aspects of the more complex scenario observed in humans. Indeed, exposome-related dyslipidemia/atherosclerosis research in zebrafish may target different scientific questions, related to nutrition, microbiota, temperature, light exposure at the larval stage, exposure to chemicals and epigenetic consequences of such external factors. Addressing genetic features related to dyslipidemia/atherosclerosis using the zebrafish model is already a reality and active research is now ongoing in this promising area. Novel technologies (gene and genome editing) may help to identify new candidate genes involved in dyslipidemia and dyslipidemia-related diseases. Based on these considerations, the zebrafish experimental model appears highly suitable for the study of exposome factors, genes and molecules involved in the development of atherosclerosis-related disease as well as for the validation of novel potential treatment options.

Zebrafish as a tractable model of human cardiovascular disease

Mammalian models including non-human primates, pigs and rodents have been used extensively to study the mechanisms of cardiovascular disease. However, there is an increasing desire for alternative model systems that provide excellent scientific value while replacing or reducing the use of mammals. Here, we review the use of zebrafish, Danio rerio, to study cardiovascular development and disease. The anatomy and physiology of zebrafish and mammalian cardiovascular systems are compared, and we describe the use of zebrafish models in studying the mechanisms of cardiac (e.g. congenital heart defects, cardiomyopathy, conduction disorders and regeneration) and vascular (endothelial dysfunction and atherosclerosis, lipid metabolism, vascular ageing, neurovascular physiology and stroke) pathologies. We also review the use of zebrafish for studying pharmacological responses to cardiovascular drugs and describe several features of zebrafish that make them a compelling model for in vivo screening of compounds for the treatment cardiovascular disease. LINKED ARTICLES: This article is part of a themed issue on Preclinical Models for Cardiovascular disease research (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.5/issuetoc.

Imaging cytoplasmic lipid droplets in vivo with fluorescent perilipin 2 and perilipin 3 knock-in zebrafish

Cytoplasmic lipid droplets are highly dynamic storage organelles that are critical for cellular lipid homeostasis. While the molecular details of lipid droplet dynamics are a very active area of investigation, this work has been primarily performed in cultured cells. Taking advantage of the powerful transgenic and in vivo imaging opportunities available in zebrafish, we built a suite of tools to study lipid droplets in real time from the subcellular to the whole organism level. Fluorescently tagging the lipid droplet-associated proteins, perilipin 2 and perilipin 3, in the endogenous loci permits visualization of lipid droplets in the intestine, liver, and adipose tissue. Using these tools, we found that perilipin 3 is rapidly loaded on intestinal lipid droplets following a high-fat meal and later replaced by perilipin 2. These powerful new tools will facilitate studies on the role of lipid droplets in different tissues, under different genetic and physiological manipulations, and in a variety of human disease models.

Intraperitoneal injection of genistein affects the distribution and metabolism of cholesterol in female yellow catfish Tachysurus fulvidraco

Genistein is an abundant phytoestrogen in soybean. This study aimed to determine the effects of genistein on cholesterol distribution and metabolism in female yellow catfish. Three hundred fish (49.2 ± 1.4 g) were randomly divided into five treatments and received intraperitoneal injections as follows: (1) blank, no injection; (2) control, vehicle only; (3) E2, 17β-estradiol at 10 μg·g^-1 body weight; (4) low genistein doses, genistein at 10 μg·g^-1 body weight; (5) high genistein doses, genistein at 100 μg·g^-1 body weight. Both high and low genistein doses significantly reduced (p < 0.05) serum TC and LDL-C 24 h after injection. Moreover, the high genistein doses significantly reduced (p < 0.05) serum HDL-C. Both high and low doses of genistein significantly increased (p < 0.05) hepatic TC. Only high genistein doses significantly increased (p < 0.05) ovary TC. In the liver, both high and low genistein doses significantly increased (p < 0.05) protein and mRNA expression of ldlr. Meanwhile, high genistein doses significantly decreased (p < 0.05) mRNA expression of hmgcr. In ovary tissue, high genistein doses significantly decreased (p < 0.05) mRNA expression of cyp11a1. These results suggested that genistein affected the cholesterol distribution in female yellow catfish. Both high and low doses of genistein reduced cholesterol content in blood and increased its content in the liver by increasing the uptake of blood cholesterol. Meanwhile, high genistein doses may inhibit hepatic cholesterol synthesis. Additionally, high genistein doses could increase cholesterol transfer from serum into the ovary and disturb cholesterol conversion to pregnenolone.

Zebrafish as a Model for the Study of Lipid-Lowering Drug-Induced Myopathies

Drug-induced myopathies are classified as acquired myopathies caused by exogenous factors. These pathological conditions develop in patients without muscle disease and are triggered by a variety of medicaments, including lipid-lowering drugs (LLDs) such as statins, fibrates, and ezetimibe. Here we summarise the current knowledge gained via studies conducted using various models, such as cell lines and mammalian models, and compare them with the results obtained in zebrafish (Danio rerio) studies. Zebrafish have proven to be an excellent research tool for studying dyslipidaemias as a model of these pathological conditions. This system enables in-vivo characterization of drug and gene candidates to further the understanding of disease aetiology and develop new therapeutic strategies. Our review also considers important environmental issues arising from the indiscriminate use of LLDs worldwide. The widespread use and importance of drugs such as statins and fibrates justify the need for the meticulous study of their mechanism of action and the side effects they cause.

Zebrafish, an In Vivo Platform to Screen Drugs and Proteins for Biomedical Use

The nearly simultaneous convergence of human genetics and advanced molecular technologies has led to an improved understanding of human diseases. At the same time, the demand for drug screening and gene function identification has also increased, albeit time- and labor-intensive. However, bridging the gap between in vitro evidence from cell lines and in vivo evidence, the lower vertebrate zebrafish possesses many advantages over higher vertebrates, such as low maintenance, high fecundity, light-induced spawning, transparent embryos, short generation interval, rapid embryonic development, fully sequenced genome, and some phenotypes similar to human diseases. Such merits have popularized the zebrafish as a model system for biomedical and pharmaceutical studies, including drug screening. Here, we reviewed the various ways in which zebrafish serve as an in vivo platform to perform drug and protein screening in the fields of rare human diseases, social behavior and cancer studies. Since zebrafish mutations faithfully phenocopy many human disorders, many compounds identified from zebrafish screening systems have advanced to early clinical trials, such as those for Adenoid cystic carcinoma, Dravet syndrome and Diamond-Blackfan anemia. We also reviewed and described how zebrafish are used to carry out environmental pollutant detection and assessment of nanoparticle biosafety and QT prolongation.

To be or not to be: endothelial cell plasticity in development, repair, and disease

Endothelial cells display an extraordinary plasticity both during development and throughout adult life. During early development, endothelial cells assume arterial, venous, or lymphatic identity, while selected endothelial cells undergo additional fate changes to become hematopoietic progenitor, cardiac valve, and other cell types. Adult endothelial cells are some of the longest-lived cells in the body and their participation as stable components of the vascular wall is critical for the proper function of both the circulatory and lymphatic systems, yet these cells also display a remarkable capacity to undergo changes in their differentiated identity during injury, disease, and even normal physiological changes in the vasculature. Here, we discuss how endothelial cells become specified during development as arterial, venous, or lymphatic endothelial cells or convert into hematopoietic stem and progenitor cells or cardiac valve cells. We compare findings from in vitro and in vivo studies with a focus on the zebrafish as a valuable model for exploring the signaling pathways and environmental cues that drive these transitions. We also discuss how endothelial plasticity can aid in revascularization and repair of tissue after damage- but may have detrimental consequences under disease conditions. By better understanding endothelial plasticity and the mechanisms underlying endothelial fate transitions, we can begin to explore new therapeutic avenues.

Recent Application of Zebrafish Models in Atherosclerosis Research

Atherosclerotic cardiovascular disease is one of the leading causes of death worldwide. Establishing animal models of atherosclerosis is of great benefit for studying its complicated pathogenesis and screening and evaluating related drugs. Although researchers have generated a variety of models for atherosclerosis study in rabbits, mice and rats, the limitations of these models make it difficult to monitor the development of atherosclerosis, and these models are unsuitable for large scale screening of potential therapeutic targets. On the contrast, zebrafish can fulfill these purposes thanks to their fecundity, rapid development ex utero, embryonic transparency, and conserved lipid metabolism process. Thus, zebrafish have become a popular alternative animal model for atherosclerosis research. In this mini review, we summarize different zebrafish models used to study atherosclerosis, focusing on the latest applications of these models to the dynamic monitoring of atherosclerosis progression, mechanistic study of therapeutic intervention and drug screening, and assessment of the impacts of other risk factors.

A Great Catch for Investigating Inborn Errors of Metabolism-Insights Obtained from Zebrafish

Inborn errors of metabolism cause abnormal synthesis, recycling, or breakdown of amino acids, neurotransmitters, and other various metabolites. This aberrant homeostasis commonly causes the accumulation of toxic compounds or depletion of vital metabolites, which has detrimental consequences for the patients. Efficient and rapid intervention is often key to survival. Therefore, it requires useful animal models to understand the pathomechanisms and identify promising therapeutic drug targets. Zebrafish are an effective tool to investigate developmental mechanisms and understanding the pathophysiology of disorders. In the past decades, zebrafish have proven their efficiency for studying genetic disorders owing to the high degree of conservation between human and zebrafish genes. Subsequently, several rare inherited metabolic disorders have been successfully investigated in zebrafish revealing underlying mechanisms and identifying novel therapeutic targets, including methylmalonic acidemia, Gaucher’s disease, maple urine disorder, hyperammonemia, TRAPPC11-CDGs, and others. This review summarizes the recent impact zebrafish have made in the field of inborn errors of metabolism.

Dare to Compare. Development of Atherosclerotic Lesions in Human, Mouse, and Zebrafish

Cardiovascular diseases, such as atherosclerosis, are the leading cause of death worldwide. Although mice are currently the most commonly used model for atherosclerosis, zebrafish are emerging as an alternative, especially for inflammatory and lipid metabolism studies. Here, we review the history of in vivo atherosclerosis models and highlight the potential for future studies on inflammatory responses in lipid deposits in zebrafish, based on known immune reactions in humans and mice, in anticipation of new zebrafish models with more advanced atherosclerotic plaques.

Zebrafish as a preclinical in vivo screening model for nanomedicines

The interactions of nanomedicines with biological environments is heavily influenced by their physicochemical properties. Formulation design and optimization are therefore key steps towards successful nanomedicine development. Unfortunately, detailed assessment of nanomedicine formulations, at a macromolecular level, in rodents is severely limited by the restricted imaging possibilities within these animals. Moreover, rodent in vivo studies are time consuming and expensive, limiting the number of formulations that can be practically assessed in any one study. Consequently, screening and optimisation of nanomedicine formulations is most commonly performed in surrogate biological model systems, such as human-derived cell cultures. However, despite the time and cost advantages of classical in vitro models, these artificial systems fail to reflect and mimic the complex biological situation a nanomedicine will encounter in vivo. This has acutely hampered the selection of potentially successful nanomedicines for subsequent rodent in vivo studies. Recently, zebrafish have emerged as a promising in vivo model, within nanomedicine development pipelines, by offering opportunities to quickly screen nanomedicines under in vivo conditions and in a cost-effective manner so as to bridge the current gap between in vitro and rodent studies. In this review, we outline several advantageous features of the zebrafish model, such as biological conservation, imaging modalities, availability of genetic tools and disease models, as well as their various applications in nanomedicine development. Critical experimental parameters are discussed and the most beneficial applications of the zebrafish model, in the context of nanomedicine development, are highlighted.

On Zebrafish Disease Models and Matters of the Heart

Coronary artery disease (CAD) is the leading form of cardiovascular disease (CVD), which is the primary cause of mortality worldwide. It is a complex disease with genetic and environmental risk factor contributions. Reports in human and mammalian models elucidate age-associated changes in cardiac function. The diverse mechanisms involved in cardiac diseases remain at the center of the research interest to identify novel strategies for prevention and therapy. Zebrafish (Danio rerio) have emerged as a valuable vertebrate model to study cardiovascular development over the last few decades. The facile genetic manipulation via forward and reverse genetic approaches combined with noninvasive, high-resolution imaging and phenotype-based screening has provided new insights to molecular pathways that orchestrate cardiac development. Zebrafish can recapitulate human cardiac pathophysiology due to gene and regulatory pathways conservation, similar heart rate and cardiac morphology and function. Thus, generations of zebrafish models utilize the functional analysis of genes involved in CAD, which are derived from large-scale human population analysis. Here, we highlight recent studies conducted on cardiovascular research focusing on the benefits of the combination of genome-wide association studies (GWAS) with functional genomic analysis in zebrafish. We further summarize the knowledge obtained from zebrafish studies that have demonstrated the architecture of the fundamental mechanisms underlying heart development, homeostasis and regeneration at the cellular and molecular levels.

Analysis of mycobacterial infection-induced changes to host lipid metabolism in a zebrafish infection model reveals a conserved role for LDLR in infection susceptibility

Changes to lipid metabolism are well-characterised consequences of human tuberculosis infection but their functional relevance are not clearly elucidated in these or other host-mycobacterial systems. The zebrafish-Mycobacterium marinum infection model is used extensively to model many aspects of human-M. tuberculosis pathogenesis but has not been widely used to study the role of infection-induced lipid metabolism. We find mammalian mycobacterial infection-induced alterations in host Low Density Lipoprotein metabolism are conserved in the zebrafish model of mycobacterial pathogenesis. Depletion of LDLR, a key lipid metabolism node, decreased M. marinum burden, and corrected infection-induced altered lipid metabolism resulting in decreased LDL and reduced the rate of macrophage transformation into foam cells. Our results demonstrate a conserved role for infection-induced alterations to host lipid metabolism, and specifically the LDL-LDLR axis, across host-mycobacterial species pairings.