montalcino, A zebrafish model for variegate porphyria

CRISPR/Cas9-Mediated fech Knockout Zebrafish: Unraveling the Pathogenesis of Erythropoietic Protoporphyria and Facilitating Drug Screening

Erythropoietic protoporphyria (EPP1) results in painful photosensitivity and severe liver damage in humans due to the accumulation of fluorescent protoporphyrin IX (PPIX). While zebrafish (Danio rerio) models for porphyria exist, the utility of ferrochelatase (fech) knockout zebrafish, which exhibit EPP, for therapeutic screening and biological studies remains unexplored. This study investigated the use of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated fech-knockout zebrafish larvae as a model of EPP1 for drug screening. CRISPR/Cas9 was employed to generate fech-knockout zebrafish larvae exhibiting morphological defects without lethality prior to 9 days post-fertilization (dpf). To assess the suitability of this model for drug screening, ursodeoxycholic acid (UDCA), a common treatment for cholestatic liver disease, was employed. This treatment significantly reduced PPIX fluorescence and enhanced bile-secretion-related gene expression (abcb11a and abcc2), indicating the release of PPIX. Acridine orange staining and quantitative reverse transcription polymerase chain reaction analysis of the bax/bcl2 ratio revealed apoptosis in fech-/- larvae, and this was reduced by UDCA treatment, indicating suppression of the intrinsic apoptosis pathway. Neutral red and Sudan black staining revealed increased macrophage and neutrophil production, potentially in response to PPIX-induced cell damage. UDCA treatment effectively reduced macrophage and neutrophil production, suggesting its potential to alleviate cell damage and liver injury in EPP1. In conclusion, CRISPR/Cas9-mediated fech-/- zebrafish larvae represent a promising model for screening drugs against EPP1.

Congenital asplenia impairs heme-iron recycling during erythropoiesis in zebrafish

The spleen is postulated to be a hematopoietic tissue in adult fish; however, clear evidence is still lacking to define its role in hematopoietic activity. In our previous study, a congenitally asplenic zebrafish was generated though gene editing, which provided a new perspective for studying the role of fish spleen in hematopoiesis. In this study, HSC-regulated and erythrocyte marker genes, such as gata1a, gata2, klf1, hbaa1, hbaa2, hbba1 and hbba2 were significantly reduced in congenitally asplenic zebrafish when compared with wild-type (WT). Subsequently, we conducted the transcriptome profiles of whole kidneys from WT and congenitally asplenic zebrafish to explore the possible molecular mechanisms underlying the impaired erythropoiesis caused by congenital asplenia. Our results demonstrated that congenital asplenia might impair heme-iron recycling during erythropoiesis, as evidenced by significant down-regulation of genes associated with iron acquisition (tfr1a, tfa, steap3 and slc25a37) and heme biosynthesis and transport (alas2, fech, uros, urod, copx, ppox and abcb10) in congenitally asplenic zebrafish. In addition, the down-regulation of hemopoiesis-related GO terms, including heme binding, tetrapyrrole binding, iron ion binding, heme metabolic process, heme biosynthetic process, erythrocyte differentiation, iron ion homeostasis and hemoglobin metabolic process confirmed the impaired erythropoiesis induced by congenital asplenia. Our study provides an in-depth understanding of spleen function in regulating heme-iron homeostasis during hematopoiesis, thereby providing valuable insights into pathological responses in splenectomized or congenitally asplenic patients.

Generation and characterization of human U-2 OS cell lines with the CRISPR/Cas9-edited protoporphyrinogen oxidase IX gene

In humans, disruptions in the heme biosynthetic pathway are associated with various types of porphyrias, including variegate porphyria that results from the decreased activity of protoporphyrinogen oxidase IX (PPO; E.C.1.3.3.4), the enzyme catalyzing the penultimate step of the heme biosynthesis. Here we report the generation and characterization of human cell lines, in which PPO was inactivated using the CRISPR/Cas9 system. The PPO knock-out (PPO-KO) cell lines are viable with the normal proliferation rate and show massive accumulation of protoporphyrinogen IX, the PPO substrate. Observed low heme levels trigger a decrease in the amount of functional heme containing respiratory complexes III and IV and overall reduced oxygen consumption rates. Untargeted proteomics further revealed dysregulation of 22 cellular proteins, including strong upregulation of 5-aminolevulinic acid synthase, the major regulatory protein of the heme biosynthesis, as well as additional ten targets with unknown association to heme metabolism. Importantly, knock-in of PPO into PPO-KO cells rescued their wild-type phenotype, confirming the specificity of our model. Overall, our model system exploiting a non-erythroid human U-2 OS cell line reveals physiological consequences of the PPO ablation at the cellular level and can serve as a tool to study various aspects of dysregulated heme metabolism associated with variegate porphyria.

The Function and the Affecting Factors of the Zebrafish Gut Microbiota

Gut microbiota has become a topical issue in unraveling the research mechanisms underlying disease onset and progression. As an important and potential "organ," gut microbiota plays an important role in regulating intestinal epithelial cell differentiation, proliferation, metabolic function and immune response, angiogenesis and host growth. More recently, zebrafish models have been used to study the interactions between gut microbiota and hosts. It has several advantages, such as short reproductive cycle, low rearing cost, transparent larvae, high genomic similarity to humans, and easy construction of germ-free (GF) and transgenic zebrafish. In our review, we reviewed a large amount of data focusing on the close relationship between gut microbiota and host health. Moreover, we outlined the functions of gut microbiota in regulating intestinal epithelial cell differentiation, intestinal epithelial cell proliferation, metabolic function, and immune response. More, we summarized major factors that can influence the composition, abundance, and diversity of gut microbiota, which will help us to understand the significance of gut microbiota in regulating host biological functions and provide options for maintaining the balance of host health.

Zebrafish as a model system to delineate the role of heme and iron metabolism during erythropoiesis

Coordination of iron acquisition and heme synthesis is required for effective erythropoiesis. The small teleost zebrafish (Danio rerio) is an ideal vertebrate animal model to replicate various aspects of human physiology and provides an efficient and cost-effective way to model human pathophysiology. Importantly, zebrafish erythropoiesis largely resembles mammalian erythropoiesis. Gene discovery by large-scale forward mutagenesis screening has identified key components in heme and iron metabolism. Reverse genetic screens, using morpholino-knockdown and CRISPR/Cas9, coupled with the genetic tractability of the developing embryo have further accelerated functional studies. Ultimately, the ex utero development of zebrafish embryos combined with their transparency and developmental plasticity could provide a deeper understanding of the role of iron and heme metabolism during early vertebrate embryonic development.

Porphyrin-Induced Protein Oxidation and Aggregation as a Mechanism of Porphyria-Associated Cell Injury

Genetic porphyrias comprise eight diseases caused by defects in the heme biosynthetic pathway that lead to accumulation of heme precursors. Consequences of porphyria include photosensitivity, liver damage and increased risk of hepatocellular carcinoma, and neurovisceral involvement, including seizures. Fluorescent porphyrins that include protoporphyrin-IX, uroporphyrin and coproporphyrin, are photo-reactive; they absorb light energy and are excited to high-energy singlet and triplet states. Decay of the porphyrin excited to ground state releases energy and generates singlet oxygen. Porphyrin-induced oxidative stress is thought to be the major mechanism of porphyrin-mediated tissue damage. Although this explains the acute photosensitivity in most porphyrias, light-induced porphyrin-mediated oxidative stress does not account for the effect of porphyrins on internal organs. Recent findings demonstrate the unique role of fluorescent porphyrins in causing subcellular compartment-selective protein aggregation. Porphyrin-mediated protein aggregation associates with nuclear deformation, cytoplasmic vacuole formation and endoplasmic reticulum dilation. Porphyrin-triggered proteotoxicity is compounded by inhibition of the proteasome due to aggregation of some of its subunits. The ensuing disruption in proteostasis also manifests in cell cycle arrest coupled with aggregation of cell proliferation-related proteins, including PCNA, cdk4 and cyclin B1. Porphyrins bind to native proteins and, in presence of light and oxygen, oxidize several amino acids, particularly methionine. Noncovalent interaction of oxidized proteins with porphyrins leads to formation of protein aggregates. In internal organs, particularly the liver, light-independent porphyrin-mediated protein aggregation occurs after secondary triggers of oxidative stress. Thus, porphyrin-induced protein aggregation provides a novel mechanism for external and internal tissue damage in porphyrias that involve fluorescent porphyrin accumulation.

Loss of Leucyl-tRNA synthetase b leads to ILFS1-like symptoms in zebrafish

Leucyl-tRNA synthetase (LARS) is a kind of aminoacyl-tRNA synthetases (aaRSs), which is important for protein synthesis. Following the discovery of three clinical cases which carry LARS mutations, it has been designated as the infantile liver failure syndrome type 1 (ILFS1) gene. ILFS1 is a kind of infantile hepatopathy, which is difficult to diagnose and manage. As the mechanism underlying this disease is poorly understood and LARS is conserved among vertebrates, we obtained zebrafish larsb^cq68 mutant via CRISPR/Cas9 technology to investigate the role of larsb in vivo. In mutant, the proliferation ability of liver was drastically decreased at later stages accompanied with severe DNA damage. Further studies demonstrated that the mTORC1 signaling was hyperactivated in larsb^cq68 mutant. Inhibition of mTORC1 signaling pathway by Rapamycin or mTORC1 morpholino can partially rescue the liver failure of the mutants. These data revealed that larsb mutation caused ILFS1-like phenotype in zebrafish, and indicated this mutant may serve as a potential model for ILFS1. Furthermore, we demonstrated that rapamycin treatment can partially rescue the liver defect in mutants, thus providing a practicable therapeutic plan for ILFS1.

TP53 Modulates Oxidative Stress in Gata1+ Erythroid Cells

Metabolism of oxidative stress is necessary for cellular survival. We have previously utilized the zebrafish as a model of the oxidative stress response. In this study, we found that gata1-expressing erythroid cells contributed to a significant proportion of total-body oxidative stress when animals were exposed to a strong pro-oxidant. RNA-seq of zebrafish under oxidative stress revealed the induction of tp53. Zebrafish carrying tp53 with a mutation in its DNA-binding domain were acutely sensitive to pro-oxidant exposure and displayed significant reactive oxygen species (ROS) and tp53-independent erythroid cell death resulting in an edematous phenotype. We found that a major contributing factor to ROS was increased basal mitochondrial respiratory rate without reserve. These data add to the concept that tp53, while classically a tumor suppressor and cell-cycle regulator, has additional roles in controlling cellular oxidative stress.

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Erythroid precursors contribute significantly to total ROS after oxidative challenge

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Tp53 is induced after pro-oxidant challenge

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Mutated tp53 is associated with an increased mitochondrial oxygen consumption rate

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Decreased mitochondrial reserve leads to overwhelming ROS and erythroid cell death

Spatiotemporal expression and transcriptional regulation of heme oxygenase and biliverdin reductase genes in zebrafish (Danio rerio) suggest novel roles during early developmental periods of heightened oxidative stress

Heme oxygenase 1 (HMOX1) degrades heme into biliverdin, which is subsequently converted to bilirubin by biliverdin reductase (BVRa or BVRb) in a manner analogous to the classic anti-oxidant glutathione-recycling pathway. To gain a better understanding of the potential antioxidant roles the BVR enzymes may play during development, the spatiotemporal expression and transcriptional regulation of zebrafish hmox1a, bvra and bvrb were characterized under basal conditions and in response to pro-oxidant exposure. All three genes displayed spatiotemporal expression patterns consistent with classic hematopoietic progenitors during development. Transient knockdown of Nrf2a did not attenuate the ability to detect bvra or bvrb by ISH, or alter spatial expression patterns in response to cadmium exposure. While hmox1a:mCherry fluorescence was documented within the intermediate cell mass, a transient location of primitive erythrocyte differentiation, expression was not fully attenuated in Nrf2a morphants, but real-time RT-PCR demonstrated a significant reduction in hmox1a expression. Furthermore, Gata-1 knockdown did not attenuate hmox1a:mCherry fluorescence. However, while there was a complete loss of detection of bvrb expression by ISH at 24hpf, bvra expression was greatly attenuated but still detectable in Gata-1 morphants. In contrast, 96 hpf Gata-1 morphants displayed increased bvra and bvrb expression within hematopoietic tissues. Finally, temporal expression patterns of enzymes involved in the generation and maintenance of NADPH were consistent with known changes in the cellular redox state during early zebrafish development. Together, these data suggest that Gata-1 and Nrf2a play differential roles in regulating the heme degradation enzymes during an early developmental period of heightened cellular stress.

Studying disorders of vertebrate iron and heme metabolism using zebrafish

Iron is a crucial component of heme- and iron-sulfur clusters, involved in vital cellular functions such as oxygen transport, DNA synthesis, and respiration. Both excess and insufficient levels of iron and heme-precursors cause human disease, such as iron-deficiency anemia, hemochromatosis, and porphyrias. Hence, their levels must be tightly regulated, requiring a complex network of transporters and feedback mechanisms. The use of zebrafish to study these pathways and the underlying genetics offers many advantages, among others their optical transparency, ex-vivo development and high genetic and physiological conservations. This chapter first reviews well-established methods, such as large-scale mutagenesis screens that have led to the initial identification of a series of iron and heme transporters and the generation of a variety of mutant lines. Other widely used techniques are based on injection of RNA, including complementary morpholino knockdown and gene overexpression. In addition, we highlight several recently developed approaches, most notably endonuclease-based gene knockouts such as TALENs or the CRISPR/Cas9 system that have been used to study how loss of function can induce human disease phenocopies in zebrafish. Rescue by chemical complementation with iron-based compounds or small molecules can subsequently be used to confirm causality of the genetic defect for the observed phenotype. All together, zebrafish have proven to be - and will continue to serve as an ideal model to advance our understanding of the pathogenesis of human iron and heme-related diseases and to develop novel therapies to treat these conditions.

Heme Mobilization in Animals: A Metallolipid's Journey

Heme is universally recognized as an essential and ubiquitous prosthetic group that enables proteins to carry out a diverse array of functions. All heme-dependent processes, from protein hemylation to heme signaling, require the dynamic and rapid mobilization of heme to hemoproteins present in virtually every subcellular compartment. The cytotoxicity and hydrophobicity of heme necessitates that heme mobilization is carefully controlled at the cellular and systemic level. However, the molecules and mechanisms that mediate heme homeostasis are poorly understood. In this Account, we provide a heuristic paradigm with which to conceptualize heme trafficking and highlight the most recent developments in the mechanisms underlying heme trafficking. As an iron-containing tetrapyrrole, heme exhibits properties of both transition metals and lipids. Accordingly, we propose its transport and trafficking will reflect principles gleaned from the trafficking of both metals and lipids. Using this conceptual framework, we follow the flow of heme from the final step of heme synthesis in the mitochondria to hemoproteins present in various subcellular organelles. Further, given that many cells and animals that cannot make heme can assimilate it intact from nutritional sources, we propose that intercellular heme trafficking pathways must exist. This necessitates that heme be able to be imported and exported from cells, escorted between cells and organs, and regulated at the organismal level via a coordinated systemic process. In this Account, we highlight recently discovered heme transport and trafficking factors and provide the biochemical foundation for the cell and systems biology of heme. Altogether, we seek to reconceptualize heme from an exchange inert cofactor buried in hemoprotein active sites to an exchange labile and mobile metallonutrient.

A precursor-inducible zebrafish model of acute protoporphyria with hepatic protein aggregation and multiorganelle stress

Protoporphyria is a metabolic disease that causes excess production of protoporphyrin IX (PP-IX), the final biosynthetic precursor to heme. Hepatic PP-IX accumulation may lead to end-stage liver disease. We tested the hypothesis that systemic administration of porphyrin precursors to zebrafish larvae results in protoporphyrin accumulation and a reproducible nongenetic porphyria model. Retro-orbital infusion of PP-IX or the iron chelator deferoxamine mesylate (DFO), with the first committed heme precursor α-aminolevulinic acid (ALA), generates high levels of PP-IX in zebrafish larvae. Exogenously infused or endogenously produced PP-IX accumulates preferentially in the liver of zebrafish larvae and peaks 1 to 3 d after infusion. Similar to patients with protoporphyria, PP-IX is excreted through the biliary system. Porphyrin accumulation in zebrafish liver causes multiorganelle protein aggregation as determined by mass spectrometry and immunoblotting. Endoplasmic reticulum stress and induction of autophagy were noted in zebrafish larvae and corroborated in 2 mouse models of protoporphyria. Furthermore, electron microscopy of zebrafish livers from larvae administered ALA + DFO showed hepatocyte autophagosomes, nuclear membrane ruffling, and porphyrin-containing vacuoles with endoplasmic reticulum distortion. In conclusion, systemic administration of the heme precursors PP-IX or ALA + DFO into zebrafish larvae provides a new model of acute protoporphyria with consequent hepatocyte protein aggregation and proteotoxic multiorganelle alterations and stress.-Elenbaas, J. S., Maitra, D., Liu, Y., Lentz, S. I., Nelson, B., Hoenerhoff, M. J., Shavit, J. A., Omary, M. B. A precursor-inducible zebrafish model of acute protoporphyria with hepatic protein aggregation and multiorganelle stress.

Epithelial cell fate in the nephron tubule is mediated by the ETS transcription factors etv5a and etv4 during zebrafish kidney development

Kidney development requires the differentiation and organization of discrete nephron epithelial lineages, yet the genetic and molecular pathways involved in these events remain poorly understood. The embryonic zebrafish kidney, or pronephros, provides a simple and useful model to study nephrogenesis. The pronephros is primarily comprised of two types of epithelial cells: transportive and multiciliated cells (MCCs). Transportive cells occupy distinct tubule segments and are characterized by the expression of various solute transporters, while MCCs function in fluid propulsion and are dispersed in a "salt-and-pepper" fashion within the tubule. Epithelial cell identity is reliant on interplay between the Notch signaling pathway and retinoic acid (RA) signaling, where RA promotes MCC fate by inhibiting Notch activity in renal progenitors, while Notch acts downstream to trigger transportive cell formation and block adoption of an MCC identity. Previous research has shown that the transcription factor ets variant 5a (etv5a), and its closely related ETS family members, are required for ciliogenesis in other zebrafish tissues. Here, we mapped etv5a expression to renal progenitors that occupy domains where MCCs later emerge. Thus, we hypothesized that etv5a is required for normal development of MCCs in the nephron. etv5a loss of function caused a decline of MCC number as indicated by the reduced frequency of cells that expressed the MCC-specific markers outer dense fiber of sperm tails 3b (odf3b) and centrin 4 (cetn4), where rescue experiments partially restored MCC incidence. Interestingly, deficiency of ets variant 4 (etv4), a related gene that is broadly expressed in the posterior mesoderm during somitogenesis stages, also led to reduced MCC numbers, which were further reduced by dual etv5a/4 deficiency, suggesting that both of these ETS factors are essential for MCC formation and that they also might have redundant activities. In epistatic studies, exogenous RA treatment expanded the etv5a domain within the renal progenitor field and RA inhibition blocked etv5a in this populace, indicating that etv5a acts downstream of RA. Additionally, treatment with exogenous RA partially rescued the reduced MCC phenotype after loss of etv5a. Further, abrogation of Notch with the small molecule inhibitor DAPT increased the renal progenitor etv5a expression domain as well as MCC density in etv5a deficient embryos, suggesting Notch acts upstream to inhibit etv5a. In contrast, etv4 levels in renal progenitors were unaffected by changes in RA or Notch signaling levels, suggesting a possible non-cell autonomous role during pronephros formation. Taken together, these findings have revealed new insights about the genetic mechanisms of epithelial cell development during nephrogenesis.

Fishing the targets of myeloid malignancies in the era of next generation sequencing

Recent advent in next generation sequencing (NGS) and bioinformatics has generated an unprecedented amount of genetic information in myeloidmalignancies. This information may shed lights to the pathogenesis, diagnosis and prognostication of these diseases and provide potential targets for therapeutic intervention. However, the rapid emergence of genetic information will quickly outpace their functional validation by conventional laboratory platforms. Foundational knowledge about zebrafish hematopoiesis accumulated over the past two decades and novel genomeediting technologies and research strategies in thismodel organismhavemade it a unique and timely research tool for the study of human blood diseases. Recent studies modeling human myeloid malignancies in zebrafish have also highlighted the technical feasibility and clinical relevance of thesemodels. Careful validation of experimental protocols and standardization among laboratorieswill further enhance the application of zebrafish in the scientific communities and provide important insights to the personalized treatment ofmyeloid malignancies.

Butafenacil: A positive control for identifying anemia- and variegate porphyria-inducing chemicals

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Butafenacil-induced anemia occurs in the presence or absence of light.

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Butafenacil-induced protoporphyrin accumulation only occurs in the presence of light.

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Embryonic zebrafish are not susceptible to butafenacil exposure following completion of pharyngula.

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Zebrafish embryos require >24 h to eliminate and recover from protoporphyrin accumulation following exposure to butafenacil during pharyngula.

Butafenacil is an herbicide that inhibits protoporphyrinogen oxidase (PPOX), an enzyme that catalyzes oxidation of protoporphyrinogen IX to protoporphyrin IX during chlorophyll and heme biosynthesis. Based on a high-content screen, we previously identified butafenacil as a potent inducer of anemia in zebrafish embryos. Therefore, the objective of this study was to begin investigating the utility of butafenacil as a positive control for identifying anemia- and variegate porphyria-inducing chemicals. Static exposure to butafenacil from 5 to 72 h post-fertilization (hpf) in glass beakers resulted in a concentration-dependent decrease in arterial circulation at low micromolar concentrations. At 72 hpf, the magnitude of butafenacil-induced anemia was similar when embryos were exposed in the presence or absence of light, whereas protoporphyrin accumulation and acute toxicity were significantly lower or absent when embryos were exposed under dark conditions. To identify sensitive developmental windows, we treated embryos to butafenacil from 5, 10, 24, or 48 hpf to 72 hpf in the presence of light, and found that anemia and protoporphyrin accumulation were present at 72 hpf following initiation of exposure at 5 and 10 hpf. On the contrary, protoporphyrin accumulation – but not anemia – was present following initiation of exposure at 24 hpf. Lastly, protoporphyrin accumulation at 72 hpf after exposure from 24 to 48 hpf suggests that protoporphyrin was not eliminated over a 24-h recovery period. Collectively, our data suggests that butafenacil may be a reliable positive control for identifying anemia- and variegate porphyria-inducing chemicals.

Nephron proximal tubule patterning and corpuscles of Stannius formation are regulated by the sim1a transcription factor and retinoic acid in zebrafish

The mechanisms that establish nephron segments are poorly understood. The zebrafish embryonic kidney, or pronephros, is a simplified yet conserved genetic model to study this renal development process because its nephrons contain segments akin to other vertebrates, including the proximal convoluted and straight tubules (PCT, PST). The zebrafish pronephros is also associated with the corpuscles of Stannius (CS), endocrine glands that regulate calcium and phosphate homeostasis, but whose ontogeny from renal progenitors is largely mysterious. Initial patterning of zebrafish renal progenitors in the intermediate mesoderm (IM) involves the formation of rostral and caudal domains, the former being reliant on retinoic acid (RA) signaling, and the latter being repressed by elevated RA levels. Here, using expression profiling to gain new insights into nephrogenesis, we discovered that the gene single minded family bHLH transcription factor 1a (sim1a) is dynamically expressed in the renal progenitors-first marking the caudal domain, then becoming restricted to the proximal segments, and finally exhibiting specific CS expression. In loss of function studies, sim1a knockdown expanded the PCT and abrogated both the PST and CS populations. Conversely, overexpression of sim1a modestly expanded the PST and CS, while it reduced the PCT. These results show that sim1a activity is necessary and partially sufficient to induce PST and CS fates, and suggest that sim1a may inhibit PCT fate and/or negotiate the PCT/PST boundary. Interestingly, the sim1a expression domain in renal progenitors is responsive to altered levels of RA, suggesting that RA regulates sim1a, directly or indirectly, during nephrogenesis. sim1a deficient embryos treated with exogenous RA formed nephrons that were predominantly composed of PCT segments, but lacked the enlarged PST observed in RA treated wild-types, indicating that RA is not sufficient to rescue the PST in the absence of sim1a expression. Alternately, when sim1a knockdowns were exposed to the RA inhibitor diethylaminobenzaldehyde (DEAB), the CS was abrogated rather than expanded as seen in DEAB treated wild-types, revealing that CS formation in the absence of sim1a cannot be rescued by RA biosynthesis abrogation. Taken together, these data reveal previously unappreciated roles for sim1a in zebrafish pronephric proximal tubule and CS patterning, and are consistent with the model that sim1a acts downstream of RA to mitigate the formation of these lineages. These findings provide new insights into the genetic pathways that direct nephron development, and may have implications for understanding renal birth defects and kidney reprogramming.

High-content screening in zebrafish embryos identifies butafenacil as a potent inducer of anemia

Using transgenic zebrafish (fli1:egfp) that stably express enhanced green fluorescent protein (eGFP) within vascular endothelial cells, we recently developed and optimized a 384-well high-content screening (HCS) assay that enables us to screen and identify chemicals affecting cardiovascular development and function at non-teratogenic concentrations. Within this assay, automated image acquisition procedures and custom image analysis protocols are used to quantify body length, heart rate, circulation, pericardial area, and intersegmental vessel area within individual live embryos exposed from 5 to 72 hours post-fertilization. After ranking developmental toxicity data generated from the U.S. Environmental Protection Agency's (EPA's) zebrafish teratogenesis assay, we screened 26 of the most acutely toxic chemicals within EPA's ToxCast Phase-I library in concentration-response format (0.05–50 µM) using this HCS assay. Based on this screen, we identified butafenacil as a potent inducer of anemia, as exposure from 0.39 to 3.125 µM butafenacil completely abolished arterial circulation in the absence of effects on all other endpoints evaluated. Butafenacil is an herbicide that inhibits protoporphyrinogen oxidase (PPO) – an enzyme necessary for heme production in vertebrates. Using o-dianisidine staining, we then revealed that severe butafenacil-induced anemia in zebrafish was due to a complete loss of hemoglobin following exposure during early development. Therefore, six additional PPO inhibitors within the ToxCast Phase-I library were screened to determine whether anemia represents a common adverse outcome for these herbicides. Embryonic exposure to only one of these PPO inhibitors – flumioxazin – resulted in a similar phenotype as butafenacil, albeit not as severe as butafenacil. Overall, this study highlights the potential utility of this assay for (1) screening chemicals for cardiovascular toxicity and (2) prioritizing chemicals for future hypothesis-driven and mechanism-focused investigations within zebrafish and mammalian models.

Oceans of opportunity: exploring vertebrate hematopoiesis in zebrafish

Exploitation of the zebrafish model in hematology research has surged in recent years, becoming one of the most useful and tractable systems for understanding regulation of hematopoietic development, homeostasis, and malignancy. Despite the evolutionary distance between zebrafish and humans, remarkable genetic and phenotypic conservation in the hematopoietic system has enabled significant advancements in our understanding of blood stem and progenitor cell biology. The strengths of zebrafish in hematology research lie in the ability to perform real-time in vivo observations of hematopoietic stem, progenitor, and effector cell emergence, expansion, and function, as well as the ease with which novel genetic and chemical modifiers of specific hematopoietic processes or cell types can be identified and characterized. Further, myriad transgenic lines have been developed including fluorescent reporter systems to aid in the visualization and quantification of specified cell types of interest and cell-lineage relationships, as well as effector lines that can be used to implement a wide range of experimental manipulations. As our understanding of the complex nature of blood stem and progenitor cell biology during development, in response to infection or injury, or in the setting of hematologic malignancy continues to deepen, zebrafish will remain essential for exploring the spatiotemporal organization and integration of these fundamental processes, as well as the identification of efficacious small molecule modifiers of hematopoietic activity. In this review, we discuss the biology of the zebrafish hematopoietic system, including similarities and differences from mammals, and highlight important tools currently utilized in zebrafish embryos and adults to enhance our understanding of vertebrate hematology, with emphasis on findings that have impacted our understanding of the onset or treatment of human hematologic disorders and disease.

Modelling inborn errors of metabolism in zebrafish

The majority of human inborn errors of metabolism are fatal multisystem disorders that lack proper treatment and have a poorly understood mechanistic basis. Novel technologies are required to address this issue, and the use of zebrafish to model these diseases is an emerging field. Here we present the published zebrafish models of inborn metabolic diseases, discuss their validity, and review the novel mechanistic insights that they have provided. We also review the available methods for creating and studying zebrafish disease models, advantages and disadvantages of using this model organism, and successful examples of the use of zebrafish for drug discovery and development. Using a zebrafish to model inborn errors of metabolism in vivo, although still in its infancy, shows promise for a deeper understanding of disease pathomechanisms, onset, and progression, and also for the development of specific therapies.

Like iron in the blood of the people: the requirement for heme trafficking in iron metabolism

Heme is an iron-containing porphyrin ring that serves as a prosthetic group in proteins that function in diverse metabolic pathways. Heme is also a major source of bioavailable iron in the human diet. While the synthesis of heme has been well-characterized, the pathways for heme trafficking remain poorly understood. It is likely that heme transport across membranes is highly regulated, as free heme is toxic to cells. This review outlines the requirement for heme delivery to various subcellular compartments as well as possible mechanisms for the mobilization of heme to these compartments. We also discuss how these trafficking pathways might function during physiological events involving inter- and intra-cellular mobilization of heme, including erythropoiesis, erythrophagocytosis, heme absorption in the gut, as well as heme transport pathways supporting embryonic development. Lastly, we aim to question the current dogma that heme, in toto, is not mobilized from one cell or tissue to another, outlining the evidence for these pathways and drawing parallels to other well-accepted paradigms for copper, iron, and cholesterol homeostasis.

Zebrafish as a model system for mitochondrial biology and diseases

Animal models for studying human disease are essential to the continuing evolution of medicine. Rodent models are attractive for the obvious similarities in development and genetic makeup compared with humans, but have cost and technical limitations. The zebrafish (Danio rerio) represents an ideal alternative vertebrate model of human disease because of its high conservation of genetic information and physiological processes, inexpensive maintenance, and optical clarity facilitating direct observation. This review highlights recent advances in understanding genetic disease states associated with the dynamic organelle, the mitochondrion, using the zebrafish. Mitochondrial diseases that have been replicated in the zebrafish include those affecting the nervous and cardiovascular systems, as well as red blood cell function. Gene silencing techniques, including morpholino knockdown and transcription activator-like (TAL)-effector endonucleases, have been exploited to demonstrate how loss of function can induce human disease-like states in zebrafish. Moreover, modeling mitochondrial diseases has been facilitated greatly by the creation of transgenic fish with fluorescently labeled mitochondria for in vivo visualization of these structures. In addition, behavioral assays have been developed to examine changes in motor activity and sensory responses, particularly in larval stages. Zebrafish are poised to advance our understanding of the pathogenesis of human mitochondrial diseases beyond the current state of knowledge and provide a key tool in the development of novel therapeutic approaches to treat these conditions.

A model of glucose-6-phosphate dehydrogenase deficiency in the zebrafish

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common genetic defect and enzymopathy worldwide, affecting approximately 400 million people and causing acute hemolysis in persons exposed to prooxidant compounds such as menthol, naphthalene, antimalarial drugs, and fava beans. Mouse models have not been useful because of a lack of significant response to oxidative challenge. We turned to zebrafish (Danio rerio) embryos, which develop ex utero and are transparent, allowing visualization of hemolysis. We designed morpholinos to zebrafish g6pd that were effective in reducing gene expression as shown by Western blot and G6PD enzyme activity, resulting in a brisk hemolysis and pericardial edema secondary to anemia. Titration of the g6pd knockdown allowed us to generate embryos that displayed no overt phenotype until exposed to the prooxidant compounds 1-naphthol, menthol, or primaquine, after which they developed hemolysis and pericardial edema within 48-72 hours. We were also able to show that g6pd morphants displayed significant levels of increased oxidative stress compared with controls. We anticipate that this will be a useful model of G6PD deficiency to study hemolysis as well as oxidative stress that occurs after exposure to prooxidants, similar to what occurs in G6PD-deficient persons.

Porphyric neuropathy

Porphyric neuropathy often poses a diagnostic dilemma; it is typically associated with the hepatic porphyrias, characterized by acute life-threatening attacks of neurovisceral symptoms that mimic a range of acute medical and psychiatric conditions. The development of acute neurovisceral attacks is responsive to environmental factors, including drugs, hormones, and diet. This chapter reviews the clinical manifestations, genetics, pathophysiology, and mechanisms of neurotoxicity of the acute hepatic porphyrias. While the etiology of the neurological manifestations in the acute porphyrias remains undefined, the main hypotheses include toxicity of porphyrin precursors and deficiency of heme synthesis. These hypotheses will be discussed with reference to novel experimental models of porphyric neuropathy.

Heme metabolism and erythropoiesis

PURPOSE OF REVIEW

Heme biosynthesis requires a series of enzymatic reactions that take place in the cytosol and the mitochondria as well as the proper intercellular and intracellular trafficking of iron. Heme can also be acquired by intestinal absorption and intercellular transport. The purpose of this review is to highlight recent work on heme and iron transport with an emphasis on their relevance in erythropoiesis.

RECENT FINDINGS

Whereas the enzymes responsible for heme biosynthesis have been identified, transport mechanisms for iron, heme, or heme synthesis intermediates are only emerging. Recent studies have shed light on how these molecules are transported among various cellular compartments, as well as tissues. Much of this progress can be attributed to the use of model organisms such as S. cerevisiae, C. elegans, D. rerio, and M. musculus. Genetic studies in these models have led to the identification of several new genes involved in heme metabolism. Although our understanding has greatly improved, it is highly likely that other regulators exist and additional work is required to characterize the pathways by which heme and iron are transported within the erythron.

SUMMARY

The identification of heme and iron transport mechanisms will improve our understanding of blood development and provide new insight into human blood disorders.

Hooked! Modeling human disease in zebrafish

Zebrafish have been widely used as a model system for studying developmental processes, but in the last decade, they have also emerged as a valuable system for modeling human disease. The development and function of zebrafish organs are strikingly similar to those of humans, and the ease of creating mutant or transgenic fish has facilitated the generation of disease models. Here, we highlight the use of zebrafish for defining disease pathways and for discovering new therapies.

One ring to rule them all: trafficking of heme and heme synthesis intermediates in the metazoans

The appearance of heme, an organic ring surrounding an iron atom, in evolution forever changed the efficiency with which organisms were able to generate energy, utilize gasses and catalyze numerous reactions. Because of this, heme has become a near ubiquitous compound among living organisms. In this review we have attempted to assess the current state of heme synthesis and trafficking with a goal of identifying crucial missing information, and propose hypotheses related to trafficking that may generate discussion and research. The possibilities of spatially organized supramolecular enzyme complexes and organelle structures that facilitate efficient heme synthesis and subsequent trafficking are discussed and evaluated. Recently identified players in heme transport and trafficking are reviewed and placed in an organismal context. Additionally, older, well established data are reexamined in light of more recent studies on cellular organization and data available from newer model organisms. This article is part of a Special Issue entitled: Cell Biology of Metals.

Zebrafish embryos and larvae: a new generation of disease models and drug screens

Technological innovation has helped the zebrafish embryo gain ground as a disease model and an assay system for drug screening. Here, we review the use of zebrafish embryos and early larvae in applied biomedical research, using selected cases. We look at the use of zebrafish embryos as disease models, taking fetal alcohol syndrome and tuberculosis as examples. We discuss advances in imaging, in culture techniques (including microfluidics), and in drug delivery (including new techniques for the robotic injection of compounds into the egg). The use of zebrafish embryos in early stages of drug safety-screening is discussed. So too are the new behavioral assays that are being adapted from rodent research for use in zebrafish embryos, and which may become relevant in validating the effects of neuroactive compounds such as anxiolytics and antidepressants. Readouts, such as morphological screening and cardiac function, are examined. There are several drawbacks in the zebrafish model. One is its very rapid development, which means that screening with zebrafish is analogous to "screening on a run-away train." Therefore, we argue that zebrafish embryos need to be precisely staged when used in acute assays, so as to ensure a consistent window of developmental exposure. We believe that zebrafish embryo screens can be used in the pre-regulatory phases of drug development, although more validation studies are needed to overcome industry scepticism. Finally, the zebrafish poses no challenge to the position of rodent models: it is complementary to them, especially in early stages of drug research.

An intercellular heme-trafficking protein delivers maternal heme to the embryo during development in C. elegans

Extracellular free heme can intercalate into membranes and promote damage to cellular macromolecules. Thus it is likely that specific intercellular pathways exist for the directed transport, trafficking, and delivery of heme to cellular destinations, although none have been found to date. Here we show that Caenorhabditis elegans HRG-3 is required for the delivery of maternal heme to developing embryos. HRG-3 binds heme and is exclusively secreted by maternal intestinal cells into the interstitial fluid for transport of heme to extraintestinal cells, including oocytes. HRG-3 deficiency results either in death during embryogenesis or in developmental arrest immediately post-hatching-phenotypes that are fully suppressed by maternal but not zygotic hrg-3 expression. Our results establish a role for HRG-3 as an intercellular heme-trafficking protein.

The acute hepatic porphyrias: current status and future challenges

The porphyrias are predominantly inherited metabolic disorders, which result from a specific deficiency of one of the eight enzymes along the pathway of haem biosynthesis. Historically, they have been classified into hepatic and erythropoietic forms, based on the primary site of expression of the prevailing dysfunctional enzyme. From a clinical point of view, however, it is more convenient to subdivide them into acute and non-acute porphyrias, thereby primarily considering the potential occurrence of life-threatening acute neurovisceral attacks. Unrecognised or untreated, such an acute porphyric attack is associated with a significant mortality of up to 10%. The acute hepatic porphyrias comprise acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and δ-aminolevulinic acid dehydratase deficiency porphyria. Making a precise diagnosis may be difficult because the different types of porphyrias may show overlapping clinical and biochemical characteristics. To date, the therapeutic possibilities are limited and mainly symptomatic. In this overview we report on what is currently known about pathogenesis, clinic, diagnostics, and therapy of the acute hepatic porphyrias. We further point out actual and future challenges in the management of these diseases.

PEI grafted hyperbranched polymers with polyglycerol as a core for gene delivery

Hyperbranched polymers, PG6-PEI25k and PG6-PEI800, were synthesized through grafting branched polyethylenimines (PEIs) with molecular weights of 25 kDa and 800 Da to a polyglycerol core (PG6), respectively. The structure of the polymers was characterized by 1H NMR and FTIR. Through agarose gel electrophoresis retardation assay, PG6-PEI25k and PG6-PEI800 were demonstrated to have capability for DNA binding. PG6-PEI/DNA complexes with different weight ratios were characterized by TEM and particle size analysis. The activity of PG6-PEIs to mediate transfection of reporter plasmids pEGFP-C1 and pGL3-Luc was evaluated on 293T and HeLa cell lines. PG6-PEI25k and PG6-PEI800 showed enhanced levels in transgene expression and decreased cytotoxicities as compared with PEI25k and PEI800, respectively. The results indicated potential applications of PG6-PEIs for efficient gene delivery.