Mapping glutathione utilization in the developing zebrafish (Danio rerio) embryo

Harnessing Simple Animal Models to Decode Sleep Mysteries

Whether it involves human subjects or non-human animals, basic, translational, or clinical sleep research poses significant ethical challenges for researchers and ethical committees alike. Sleep research greatly benefits from using diverse animal models, each offering unique insights into sleep control mechanisms. The fruit fly (Drosophila melanogaster) is a superior genetic model due to its quick generation period, large progenies, and rich genetic tools. Its well-characterized genome and ability to respond to hypnotics and stimulants make it an effective tool for studying sleep genetics and physiological foundations. The nematode (Caenorhabditis elegans) has a simpler neural organization and transparent body, allowing researchers to explore molecular underpinnings of sleep control. Vertebrate models, like zebrafish (Danio rerio), provide insights into circadian rhythm regulation, memory consolidation, and drug effects on sleep. Invertebrate models, like California sea hare (Aplysia californica) and Upside-down jellyfish (Cassiopea xamachana), have simpler nervous systems and behave similarly to humans, allowing for the examination of sleep principles without logistical and ethical challenges. Combining vertebrate and invertebrate animal models offers a comprehensive approach to studying sleep, improving our understanding of sleep regulation and potentially leading to new drug discovery processes for sleep disorders and related illnesses.

Dynamics of Redox Metabolism during Complete Metamorphosis of Insects: Insights from the Sunflower Caterpillar Chlosyne lacinia (Lepidoptera)

Complete insect metamorphosis requires substantial metabolic and physiological adjustments. Although oxidative stress has been implicated in metamorphosis, details on redox metabolism during larva-to-pupa and pupa-to-adult remain scarce. This study explores redox metabolism during metamorphosis of a lepidopteran (Chlosyne lacinia), focusing on core metabolism, antioxidant systems and oxidative stress. The larva-to-pupa transition was characterized by increased lactate dehydrogenase and glutathione peroxidase (GPX) activities, coupled with depletion of reduced glutathione (GSH), high disulfide-to-total-glutathione ratio (GSSG/tGSH), and increased lipid peroxidation. As metamorphosis progressed, metabolic enzyme activities, citrate synthase and glucose 6-phosphate dehydrogenase increased, indicating heightened oxidative metabolism associated with adult development. Concurrently, GSH and GPX levels returned to larval levels and GSSG/tGSH reached its most reduced state right before adult emergence. Adult emergence was marked by a further increase in oxidative metabolism, accompanied by redox imbalance and enhanced antioxidant mechanisms. These findings highlight a fluctuation in redox balance throughout metamorphosis, with periods of oxidative eustress followed by compensatory antioxidant responses. This study is the first to identify concurrent changes in metabolism, antioxidants, redox balance and oxidative stress throughout metamorphosis. Our findings extend knowledge on redox metabolism adjustments and highlight redox adaptations and oxidative stress as natural components of complete insect metamorphosis.

Systemic and strict regulation of the glutathione redox state in mitochondria and cytosol is needed for zebrafish ontogeny

BACKGROUND

Redox control seems to be indispensable for proper embryonic development. The ratio between glutathione (GSH) and its oxidized disulfide (GSSG) is the most abundant cellular redox circuit.

METHODS

We used zebrafish harboring the glutaredoxin 1-redox sensitive green fluorescent protein (Grx1-roGFP) probe either in mitochondria or cytosol to test the hypothesis that the GSH:GSSG ratio is strictly regulated through zebrafish embryogenesis to sustain the different developmental processes of the embryo.

RESULTS

Following the GSSG:GSH ratio as a proxy for the GSH-dependent reduction potential (EhGSH) revealed increasing mitochondrial and cytosolic EhGSH during cleavage and gastrulation. During organogenesis, cytosolic EhGSH decreased, while that of mitochondria remained high. The similarity between EhGSH in brain and muscle suggests a central regulation. Modulation of GSH metabolism had only modest effects on the GSSG:GSH ratios of newly hatched larvae. However, inhibition of GSH reductase directly after fertilization led to dead embryos already 10 h later. Exposure to the emerging environmental pollutant Perfluorooctane Sulfonate (PFOS) disturbed the apparent regulated EhGSH as well.

CONCLUSIONS

Mitochondrial and cytosolic GSSG:GSH ratios are almost identical in different organs during zebrafish development indicating that the EhGSH might follow H2O2 levels and rather indirectly affect specific enzymatic activities needed for proper embryogenesis.

GENERAL SIGNIFICANCE

Our data confirm that vertebrate embryogenesis depends on strictly regulated redox homeostasis. Disturbance of the GSSG:GSH circuit, e.g. induced by environmental pollution, leads to malformation and death.

Developmental effects of zebrafish (Danio rerio) embryos after exposure to glyphosate and lead mixtures

Natural aquatic environments have a heterogeneous composition; therefore, simultaneous exposure to multiple contaminants is relevant and more realistic when assessing exposure and toxicity. This study examines the combinatorial effects of two compounds found ubiquitously in drinking water across the United States: glyphosate and lead acetate. Zebrafish (Danio rerio) embryos were used as a model for investigating developmental delays following controlled exposures. Six different environmentally relevant exposure concentrations of glyphosate, ranging from 0.001 to 10 ppm, and lead acetate, ranging from 0.5 to 4 ppm, were applied first as single exposures and then as co-exposures. The sublethal endpoints of hatching and coagulation were quantified to determine potencies. Results indicate that higher concentrations of the individual chemicals correlate with later hatching with correlation coefficients of 0.71 and 0.40 for glyphosate and lead acetate respectively, while the co-exposure at lower concentrations induced earlier hatching with a correlation coefficient 0.74. In addition, increased levels of coagulation and glutathione reductase activity were observed following co-exposure, as compared to the individual exposures, suggesting potential toxicological interactions. These results support the need for further work assessing the combined potencies of aquatic contaminants rather than individual exposures.

Increasing glutathione levels by a novel posttranslational mechanism inhibits neuronal hyperexcitability

Glutathione (GSH) depletion, and impaired redox homeostasis have been observed in experimental animal models and patients with epilepsy. Pleiotropic strategies that elevate GSH levels via transcriptional regulation have been shown to significantly decrease oxidative stress and seizure frequency, increase seizure threshold, and rescue certain cognitive deficits. Whether elevation of GSH per se alters neuronal hyperexcitability remains unanswered. We previously showed that thiols such as dimercaprol (DMP) elevate GSH via post-translational activation of glutamate cysteine ligase (GCL), the rate limiting GSH biosynthetic enzyme. Here, we asked if elevation of cellular GSH by DMP altered neuronal hyperexcitability in-vitro and in-vivo. Treatment of primary neuronal-glial cerebrocortical cultures with DMP elevated GSH and inhibited a voltage-gated potassium channel blocker (4-aminopyridine, 4AP) induced neuronal hyperexcitability. DMP increased GSH in wildtype (WT) zebrafish larvae and significantly attenuated convulsant pentylenetetrazol (PTZ)-induced acute 'seizure-like' swim behavior. DMP treatment increased GSH and inhibited convulsive, spontaneous 'seizure-like' swim behavior in the Dravet Syndrome (DS) zebrafish larvae (scn1Lab). Furthermore, DMP treatment significantly decreased spontaneous electrographic seizures and associated seizure parameters in scn1Lab zebrafish larvae. We investigated the role of the redox-sensitive mammalian target of rapamycin (mTOR) pathway due to the presence of several cysteine-rich proteins and their involvement in regulating neuronal excitability. Treatment of primary neuronal-glial cerebrocortical cultures with 4AP or l-buthionine-(S,R)-sulfoximine (BSO), an irreversible inhibitor of GSH biosynthesis, significantly increased mTOR complex I (mTORC1) activity which was rescued by pre-treatment with DMP. Furthermore, BSO-mediated GSH depletion oxidatively modified the tuberous sclerosis protein complex (TSC) consisting of hamartin (TSC1), tuberin (TSC2), and TBC1 domain family member 7 (TBC1D7) which are critical negative regulators of mTORC1. In summary, our results suggest that DMP-mediated GSH elevation by a novel post-translational mechanism can inhibit neuronal hyperexcitability both in-vitro and in-vivo and a plausible link is the redox sensitive mTORC1 pathway.

Rapid GSH detection and versatile peptide/protein labelling to track cell penetration using coumarin-based probes

Biothiols play essential roles in balancing the redox state and modulating cellular functions. Fluorescent probes for monitoring/labelling biothiols often suffer from slow reaction rates, strong background fluorescence and cytotoxic byproduct release. Thus, developing facile and versatile probes to overcome the challenges is still in high demand. Here, we report four coumarin-maleimides as fast responding and fluorogenic probes to detect GSH or label peptides/proteins. The probes quantitatively and selectively react with GSH via Michael addition within 1-2 min, achieving an 11-196-fold increase in fluorescence quantum yield via blockage of the photoinduced electron transfer (PET) process. Optimized probe 4 is applied for the detection of GSH in vitro (A549 cells) and in vivo (zebrafish embryos). Taking advantage of the fast Michael addition between the maleimide moiety and the sulfhydryl group, we expand the application of our method for fluorescent labelling of peptides/proteins and for tracking their cellular uptake process. The labelling strategy works for both Cys-bearing and Cys-free proteins after the introduction of a sulfhydryl group using Traut's reagent. Fluorescence assay reveals that the TAT-peptide can efficiently enter cells, but H3 protein, part of nucleosomes, prefers to bind on the cell membrane by electrostatic interactions, shedding light on the cellular uptake activity of nucleosomes and affording a potential membrane staining strategy. Overall, our study illustrates the broad potential of coumarin-maleimide based dual-functional probes for GSH detection and versatile protein labelling in biochemical research.

Developmental impacts of Nrf2 activation by dimethyl fumarate (DMF) in the developing zebrafish (Danio rerio) embryo

Dimethyl fumarate (DMF) is pharmaceutical activator of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates of many cellular antioxidant response pathways, and has been used to treat inflammatory diseases such as multiple sclerosis. However, DMF has been shown to produce adverse effects on offspring in animal studies and as such is not recommended for use during pregnancy. The goal of this work is to better understand how these adverse effects are initiated and the role of DMF-induced Nrf2 activation during three critical windows of development in embryonic zebrafish (Danio rerio): pharyngula, hatching, and protruding-mouth stages. To evaluate Nrf2 activation, wildtype zebrafish, and mutant zebrafish (nrf2afh318/fh318) embryos with a loss of function mutation in Nrf2a, the co-ortholog to human Nrf2, were treated for 6 h with DMF (0-20 μM) beginning at the pharyngula, hatching, or protruding-mouth stage and assessed for survival and morphology. Nrf2a mutant fish had an increase in survival, however, morphology studies demonstrated Nrf2a mutant fish had more severe deformities occurring with exposures during the hatching stage. To verify Nrf2 cellular localization and downstream impacts on protein-S-glutathionylation in situ, a concentration below the LOAEL was chosen (7 μM) for immunohistochemistry and S-glutathionylation. Embryos were imaged via epifluorescence microscopy studies, the Nrf2a protein in the body tissue was decreased with DMF only when exposed at the hatching stage, while total protein S-glutathionylation was modulated by Nrf2a activity and DMF during the pharyngula and protruding-mouth stage. The pancreatic islet and liver were further analyzed via confocal microscopy. Pancreatic islets and liver also had tissue specific differences with Nrf2a protein expression and protein S-glutathionylation. This work demonstrates how critical windows of exposure and Nrf2a activity may influence toxicity of DMF and highlights tissue-specific changes in Nrf2a protein levels and S-glutathionylation in pancreatic islet and liver during embryonic development.

Catechin from green tea had the potential to decrease the chlorpyrifos induced oxidative stress in larval zebrafish (Danio rerio)

Catechin is a biological compound in green tea (Camellia sinesis), which has anti-oxidant, anti-cancer, anti-apoptotic, anti-inflammatory, and attenuated effects in different experimental models. Chlorpyrifos (CPF), a broad-spectrum organophosphate insecticide, has resulted in oxidative stress, mitochondrial dysfunction, and apoptosis in zebrafish. The goal of this study is to assess whether catechin can alleviate CPF-induced oxidative damage and apoptosis in the early developmental stage of zebrafish. According to the results, we observed that 200 μg/L CPF exposure could induce oxidative stress, ROS production and changing the antioxidant-related enzymes and genes in larval zebrafish. Interestingly, catechin had the potential to reduce the oxidative damage and cell apoptosis caused by CPF exposure in larval zebrafish at different endpoints. Especially, catechin could promote the contents of GSH and activity of GST in zebrafish larvae injured by CPF, suggesting that catechin could repair oxidative damage at a certain degree by regulating the activities and gene transcription of some key enzymes related to GSH pathway in zebrafish. In addition, at transcriptional levels, a high concentration of catechin exposure reduced the expression genes of Mn-SOD, Cat, gst, and GPX induced by CPF in larval zebrafish. These genes mainly reflected the degree of oxidative damage of zebrafish, which was basically consistent with the enzyme activity. Catechin also could reduce the transcription of p53 and bax, which are tightly related to the apoptosis induced by CPF in zebrafish larvae. The expression of genes was consistent with ROS production, which proved that catechin could alleviate the apoptosis induced by CPF. This study discovered that catechin had some antioxidant effects in aquatic animals to reduce the toxicity caused by pesticides and offered the scientific basis for the utilization and development of catechin.

Oxidative damage in Nile tilapia, Oreochromis niloticus, is mainly induced by water temperature variation rather than Aurantiochytrium sp. meal dietary supplementation

We investigated whether dietary supplementation with Aurantiochytrium sp. meal, a DHA-rich source (docosahexaenoic acid, 22: 6 n-3), fed during long-term exposure to cold-suboptimal temperature (22 °C, P1), followed by short-term exposure to higher temperatures (28 °C, P2, and 33 °C, P3), would promote oxidative damage in Nile tilapia (Oreochromis niloticus). Two supplementation levels were tested: 1.0 g 100 g^-1 (D1) and 4.0 g 100 g^-1 (D4). A control diet, without the additive (D0, 0 g 100 g^-1), and a positive control diet supplemented with cod liver oil (CLO) were also tested. The concentrations of DHA and total n-3 PUFAs in the CLO diet were similar to those found in diets D1 and D4, respectively. The parameters analyzed included hemoglobin (Hb), the antioxidant enzymes catalase, glutathione peroxidase, total glutathione, non-protein thiols, and the oxidative markers protein carbonyl and erythrocyte DNA damage. Nile tilapia did not present differences in Hb content, regardless of diet composition, but the temperature increase (P1 to P2) led to a higher Hb content. Likewise, the temperature increases promoted alterations in all antioxidant enzymes. The dietary supplementation with 1.0 g 100 g^-1 Aurantiochytrium sp. meal after P1 caused minor DNA damage in Nile tilapia, demonstrating that the additive can safely be included in winter diets, despite its high DHA concentration.

The Nrf2a pathway impacts zebrafish offspring development with maternal preconception exposure to perfluorobutanesulfonic acid

Since the voluntary phaseout of perfluorooctanesulfonic acid (PFOS), smaller congeners, such as perfluorobutanesulfonic acid (PFBS) have served as industrial replacements and been detected in contaminated aquifers. This study sought to examine the effects of a maternal preconception PFBS exposure on the development of eggs and healthy offspring. Adult female zebrafish received a one-week waterborne exposure of 0.08, 0.14, and 0.25 mg/L PFBS. After which, females were bred with non-exposed males and embryos collected over 5 successful breeding events. PFBS concentrations were detected in levels ranging from 99 to 253 pg/embryo in the first collection but were below the limit of quantitation by fourth and fifth clutches. Therefore, data were subsequently binned into early collection embryos in which PFBS was detected and late collections, in which PFBS was below quantitation. In the early collection, embryo 24 h survival was significantly reduced. In the late collection, embryo development was impacted with unique patterns emerging between Nrf2a wildtype and mutant larvae. Additionally, the impact of nutrient loading into the embryos was assessed through measurement of fatty acid profiles, total cholesterol, and triglyceride content. There were no clear dose-dependent effects, but again unique patterns were observed between the genotypes. Preconception PFBS exposures were found to alter egg and embryo development, which is mediated by direct toxicant loading in the eggs, nutrient loading into eggs, and the function of Nrf2a. These findings provide insight into the reproductive and developmental effects of PFBS and identify maternal preconception as a novel critical window of exposure.

Review on Toxic Effects of Di(2-ethylhexyl) Phthalate on Zebrafish Embryos

Di(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in consumer products. People are continuously exposed to DEHP through ingestion, inhalation and dermal absorption. From epidemiological studies, DEHP has been shown to associate with various adverse health effects, such as reproductive abnormalities and metabolic diseases. Health concerns have been raised regarding DEHP exposures; therefore, relevant risk assessment has become necessary through toxicological testing of DEHP. In the past 10 years, an increasing number of DEHP toxicity studies have been using zebrafish embryos as an in vivo model due to their high fecundity, rapid embryonic development as well as optical transparency, which have now been established as an alternative of the more conventional rodent model. The aim of the present paper is to review the effects of acute (from embryo stage to ≤1 week) and chronic (from embryo stage to >1 week) DEHP exposures on zebrafish, which start from the embryonic stage, and to analyze acute and potential long-term effects induced by acute exposure and effects induced by chronic exposure of DEHP upon subjecting to exposures, starting from the embryonic stage to different developmental stages, with a view to facilitate risk assessments on DEHP exposures.

N-acetyl-cysteine and the control of oxidative stress during in vitro ovarian follicle growth, oocyte maturation, embryo development and cryopreservation

Oxidative stress is generated by an imbalance between reactive oxygen species (ROS) formation and cellular defense mechanisms. To reduce cellular damage caused by ROS in vivo or in vitro, N-acetyl-cysteine (NAC) is converted into metabolites that have the capacity of stimulating synthesis of glutathione (GSH) which functions directly as free radical scavengers. The NAC antioxidant potential evaluated to the greatest extent is the indirect action of NAC, as a precursor of GSH, with glutathione being the primary antioxidant in cells. During long-term preantral follicle culture, NAC has a synergic action with FSH and an important function in sustaining preantral follicle growth and follicle-cell viability in vitro. The NAC inclusion in in vitro maturation medium for cumulus-oocyte complexes (COC) leads to protection of oocytes from damage induced by heat stress, reductions in ROS, and increases in cumulus cell expansion. Developing embryos are susceptable to oxidative stress because of susceptability to cellular structure damage and not having well-developed defense mechanisms. Results from various indicate there are beneficial effects of NAC on embryonic development by increasing GSH biosynthesis and regulating cell proliferation. In addition, NAC is also an effective antioxidant during cryopreservation of ovarian follicles, oocytes and embryos, because inclusion of NAC in preservation medium leads to improvements in mitochondrial function and cell viability, and reductions in ROS and cellular apoptosis. In this review, there is evaluation of mechanisms of action of NAC and beneficial effects during in vitro culture of preantral follicles, as well as oocyte maturation, embryonic development and cryopreservation.

A Spatiotemporal Characterisation of Redox Molecules in Planarians, with a Focus on the Role of Glutathione during Regeneration

A strict coordination between pro- and antioxidative molecules is needed for normal animal physiology, although their exact function and dynamics during regeneration and development remains largely unknown. Via in vivo imaging, we were able to locate and discriminate between reactive oxygen species (ROS) in real-time during different physiological stages of the highly regenerative planarian Schmidtea mediterranea. All ROS signals were strong enough to overcome the detected autofluorescence. Combined with an in situ characterisation and quantification of the transcription of several antioxidant genes, our data showed that the planarian gut and epidermis have a well-equipped redox system. Pharmacological inhibition or RNA interference of either side of the redox balance resulted in alterations in the regeneration process, characterised by decreased blastema sizes and delayed neurodevelopment, thereby affecting tails more than heads. Focusing on glutathione, a central component in the redox balance, we found that it is highly present in planarians and that a significant reduction in glutathione content led to regenerative failure with tissue lesions, characterised by underlying stem cell alterations. This exploratory study indicates that ROS and antioxidants are tightly intertwined and should be studied as a whole to fully comprehend the function of the redox balance in animal physiology.

Using Monochlorobimane to Visualize Glutathione Utilization in the Developing Zebrafish (Danio rerio) Embryo

Glutathione (GSH) plays fundamental roles in cellular redox buffering and is a common detoxification pathway for excretion of xenobiotics. This is especially crucial during vertebrate embryogenesis, when an organism is at one of its most vulnerable life stages. Importantly, GSH content and redox potential can dictate cell fate decisions, which can have profound consequences if altered by early life xenobiotic exposures. Owing to technical limitations, the best available method to detect and quantify changes in GSH has been high-pressure liquid chromatography, a terminal method that prevents suborganism-level resolution of these changes in developing embryos. Here, we describe a protocol that leverages the transparent nature of zebrafish embryos and the compatibility of monochlorobimane with the zebrafish GSH-S-transferase enzymes, to allow for the visualization of changes in GSH via S-glutathionylation in a live, developing embryo. This method can find broad application in developmental biology and toxicology. © 2021 Wiley Periodicals LLC.

Oxidative eustress: On constant alert for redox homeostasis

In the open metabolic system, redox-related signaling requires continuous monitoring and fine-tuning of the steady-state redox set point. The ongoing oxidative metabolism is a persistent challenge, denoted as oxidative eustress, which operates within a physiological range that has been called the 'Homeodynamic Space', the 'Goldilocks Zone' or the 'Golden Mean'. Spatiotemporal control of redox signaling is achieved by compartmentalized generation and removal of oxidants. The cellular landscape of H₂O₂, the major redox signaling molecule, is characterized by orders-of-magnitude concentration differences between organelles. This concentration pattern is mirrored by the pattern of oxidatively modified proteins, exemplified by S-glutathionylated proteins. The review presents the conceptual background for short-term (non-transcriptional) and longer-term (transcriptional/translational) homeostatic mechanisms of stress and stress responses. The redox set point is a variable moving target value, modulated by circadian rhythm and by external influence, summarily denoted as exposome, which includes nutrition and lifestyle factors. Emerging fields of cell-specific and tissue-specific redox regulation in physiological settings are briefly presented, including new insight into the role of oxidative eustress in embryonal development and lifespan, skeletal muscle and exercise, sleep-wake rhythm, and the function of the nervous system with aspects leading to psychobiology.

Modulating glutathione thiol status alters pancreatic β-cell morphogenesis in the developing zebrafish (Danio rerio) embryo

Emerging evidence suggests that redox-active chemicals perturb pancreatic islet development. To better understand potential mechanisms for this, we used zebrafish (Danio rerio) embryos to investigate roles of glutathione (GSH; predominant cellular redox buffer) and the transcription factor Nrf2a (Nfe2l2a; zebrafish Nrf2 co-ortholog) in islet morphogenesis. We delineated critical windows of susceptibility to redox disruption of β-cell morphogenesis, interrogating embryos at 24, 48 and 72 h post fertilization (hpf) and visualized Nrf2a expression in the pancreas using whole-mount immunohistochemistry at 96 hpf. Chemical GSH modulation at 48 hpf induced significant islet morphology changes at 96 hpf. Pro-oxidant exposures to tert-butylhydroperoxide (77.6 μM; 10-min at 48 hpf) or tert-butylhydroquinone (1 μM; 48-56 hpf) decreased β-cell cluster area at 96 hpf. Conversely, exposures to antioxidant N-acetylcysteine (bolsters GSH pools; 100 μM; 48-72 hpf) or sulforaphane (activates Nrf2a; 20 μM; 48-72 hpf) significantly increased islet areas. Nrf2a was also stabilized in β-cells: 10-min exposures to 77.6 μM tert-butylhydroperoxide significantly increased Nrf2a protein compared to control islet cells that largely lack stabilized Nrf2a; 10-min exposures to higher (776 μM) tert-butylhydroperoxide concentration stabilized Nrf2a throughout the pancreas. Using biotinylated-GSH to visualize in situ protein glutathionylation, islet cells displayed high protein glutathionylation, indicating oxidized GSH pools. The 10-min high (776 μM) tert-butylhydroperoxide exposure (induced Nrf2a globally) decreased global protein glutathionylation at 96 hpf. Mutant fish expressing inactive Nrf2a were protected against tert-butylhydroperoxide-induced abnormal islet morphology. Our data indicate that disrupted redox homeostasis and Nrf2a stabilization during pancreatic β-cell development impact morphogenesis, with implications for disease states at later life stages. Our work identifies a potential molecular target (Nrf2) that mediates abnormal β-cell morphology in response to redox disruptions. Moreover, our findings imply that developmental exposure to exogenous stressors at distinct windows of susceptibility could diminish the reserve redox capacity of β-cells, rendering them vulnerable to later-life stresses and disease.