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The role of Nrf1 and Nrf2 in the regulation of glutathione and redox dynamics in the developing zebrafish embryo.

ABSTRACT: Redox signaling is important for embryogenesis, guiding pathways that govern processes crucial for embryo patterning, including cell polarization, proliferation, and apoptosis. Exposure to pro-oxidants during this period can be deleterious, resulting in altered physiology, teratogenesis, later-life diseases, or lethality. We previously reported that the glutathione antioxidant defense system becomes increasingly robust, including a doubling of total glutathione and dynamic shifts in the glutathione redox potential at specific stages during embryonic development in the zebrafish, Danio rerio. However, the mechanisms underlying these changes are unclear, as is the effectiveness of the glutathione system in ameliorating oxidative insults to the embryo at different stages. Here, we examine how the glutathione system responds to the model pro-oxidants tert-butylhydroperoxide and tert-butylhydroquinone at different developmental stages, and the role of Nuclear factor erythroid 2-related factor (Nrf) proteins in regulating developmental glutathione redox status. Embryos became increasingly sensitive to pro-oxidants after 72h post-fertilization (hpf), after which the duration of the recovery period for the glutathione redox potential was increased. To determine whether the doubling of glutathione or the dynamic changes in glutathione redox potential are mediated by zebrafish paralogs of Nrf transcription factors, morpholino oligonucleotides were used to knock down translation of Nrf1 and Nrf2 (nrf1a, nrf1b, nrf2a, nrf2b). Knockdown of Nrf1a or Nrf1b perturbed glutathione redox state until 72 hpf. Knockdown of Nrf2 paralogs also perturbed glutathione redox state but did not significantly affect the response of glutathione to pro-oxidants. Nrf1b morphants had decreased gene expression of glutathione synthesis enzymes, while hsp70 increased in Nrf2b morphants. This work demonstrates that despite having a more robust glutathione system, embryos become more sensitive to oxidative stress later in development, and that neither Nrf1 nor Nrf2 alone appear to be essential for the response and recovery of glutathione to oxidative insults.

SUBMITTER: Sant KE

PROVIDER: S-EPMC5458767 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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The role of Nrf1 and Nrf2 in the regulation of glutathione and redox dynamics in the developing zebrafish embryo.

Sant Karilyn E KE Hansen Jason M JM Williams Larissa M LM Tran Nancy L NL Goldstone Jared V JV Stegeman John J JJ Hahn Mark E ME Timme-Laragy Alicia A

Redox biology 20170530

Redox signaling is important for embryogenesis, guiding pathways that govern processes crucial for embryo patterning, including cell polarization, proliferation, and apoptosis. Exposure to pro-oxidants during this period can be deleterious, resulting in altered physiology, teratogenesis, later-life diseases, or lethality. We previously reported that the glutathione antioxidant defense system becomes increasingly robust, including a doubling of total glutathione and dynamic shifts in the glutathi ...[more]

PMID: 28582729

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Project description:Embryonic development involves dramatic changes in cell proliferation and differentiation that must be highly coordinated and tightly regulated. Cellular redox balance is critical for cell fate decisions, but it is susceptible to disruption by endogenous and exogenous sources of oxidative stress. The most abundant endogenous nonprotein antioxidant defense molecule is the tripeptide glutathione (γ-glutamylcysteinylglycine, GSH), but the ontogeny of GSH concentration and redox state during early life stages is poorly understood. Here, we describe the GSH redox dynamics during embryonic and early larval development (0-5 days postfertilization) in the zebrafish (Danio rerio), a model vertebrate embryo. We measured reduced and oxidized glutathione using HPLC and calculated the whole embryo total glutathione (GSHT) concentrations and redox potentials (Eh) over 0-120 h of zebrafish development (including mature oocytes, fertilization, midblastula transition, gastrulation, somitogenesis, pharyngula, prehatch embryos, and hatched eleutheroembryos). GSHT concentration doubled between 12h postfertilization (hpf) and hatching. The GSH Eh increased, becoming more oxidizing during the first 12h, and then oscillated around -190 mV through organogenesis, followed by a rapid change, associated with hatching, to a more negative (more reducing) Eh (-220 mV). After hatching, Eh stabilized and remained steady through 120 hpf. The dynamic changes in GSH redox status and concentration defined discrete windows of development: primary organogenesis, organ differentiation, and larval growth. We identified the set of zebrafish genes involved in the synthesis, utilization, and recycling of GSH, including several novel paralogs, and measured how expression of these genes changes during development. Ontogenic changes in the expression of GSH-related genes support the hypothesis that GSH redox state is tightly regulated early in development. This study provides a foundation for understanding the redox regulation of developmental signaling and investigating the effects of oxidative stress during embryogenesis.

Project description:Glutathione (GSH), the most abundant vertebrate endogenous redox buffer, plays key roles in organogenesis and embryonic development, however, organ-specific GSH utilization during development remains understudied. Monochlorobimane (MCB), a dye conjugated with GSH by glutathione-s-transferase (GST) to form a fluorescent adduct, was used to visualize organ-specific GSH utilization in live developing zebrafish (Danio rerio) embryos. Embryos were incubated in 20 μM MCB for 1 h and imaged on an epifluorescence microscope. GSH conjugation with MCB was high during early organogenesis, decreasing as embryos aged. The heart had fluorescence 21-fold above autofluorescence at 24 hpf, dropping to 8.5-fold by 48 hpf; this increased again by 72 hpf to 23.5-fold, and stayed high till 96 hpf (18-fold). The brain had lower fluorescence (10-fold) at 24 and 48 hpf, steadily increasing to 30-fold by 96 hpf. The sensitivity and specificity of MCB staining was then tested with known GSH modulators. A 10-min treatment at 48 hpf with 750 μM tert-butylhydroperoxide, caused organ-specific reductions in staining, with the heart losing 30% fluorescence, and, the brain ventricle losing 47% fluorescence. A 24 h treatment from 24-48 hpf with 100 μM of N-Acetylcysteine (NAC) resulted in significantly increased fluorescence, with the brain ventricle and heart showing 312% and 240% increases respectively, these were abolished upon co-treatment with 5 μM BSO, an inhibitor of the enzyme that utilizes NAC to synthesize GSH. A 60 min 100 μM treatment with ethacrynic acid, a specific GST inhibitor, caused 30% reduction in fluorescence across all measured structures. MCB staining was then applied to test for GSH disruptions caused by the toxicants perfluorooctanesulfonic acid and mono-(2-ethyl-hexyl)phthalate; MCB fluorescence responded in a dose, structure and age-dependent manner. MCB staining is a robust, sensitive method to detect spatiotemporal changes in GSH utilization, and, can be applied to identify sensitive target tissues of toxicants.

Dataset Information

The role of Nrf1 and Nrf2 in the regulation of glutathione and redox dynamics in the developing zebrafish embryo.

Publications

The role of Nrf1 and Nrf2 in the regulation of glutathione and redox dynamics in the developing zebrafish embryo.

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