Genetically encoded thiol redox-sensors in the zebrafish model: lessons for embryonic development and regeneration

Promising tools into oxidative stress: A review of non-rodent model organisms

Oxidative stress is a crucial concept in redox biology, and significant progress has been made in recent years. Excessive levels of reactive oxygen species (ROS) can lead to oxidative damage, heightening vulnerability to various diseases. By contrast, ROS maintained within a moderate range plays a role in regulating normal physiological metabolism. Choosing suitable animal models in a complex research context is critical for enhancing research efficacy. While rodents are frequently utilized in medical experiments, they pose challenges such as high costs and ethical considerations. Alternatively, non-rodent model organisms like zebrafish, Drosophila, and C. elegans offer promising avenues into oxidative stress research. These organisms boast advantages such as their small size, high reproduction rate, availability for live imaging, and ease of gene manipulation. This review highlights advancements in the detection of oxidative stress using non-rodent models. The oxidative homeostasis regulatory pathway, Kelch-like ECH-associated protein 1-Nuclear factor erythroid 2-related factor 2 (Keap1-Nrf2), is systematically reviewed alongside multiple regulation of Nrf2-centered pathways in different organisms. Ultimately, this review conducts a comprehensive comparative analysis of different model organisms and further explores the combination of novel techniques with non-rodents. This review aims to summarize state-of-the-art findings in oxidative stress research using non-rodents and to delineate future directions.

Imaging immunometabolism in situ in live animals

Immunometabolism is a rapidly developing field that holds great promise for diagnostic and therapeutic benefits to human diseases. The field has emerged based on seminal findings from in vitro and ex vivo studies that established the fundamental role of metabolism in immune cell effector functions. Currently, the field is acknowledging the necessity of investigating cellular metabolism within the natural context of biological processes. Examining cells in their native microenvironment is essential not only to reveal cell-intrinsic mechanisms but also to understand how cross-talk between neighboring cells regulates metabolism at the tissue level in a local niche. This necessity is driving innovation and advancement in multiple imaging-based technologies to enable analysis of dynamic intracellular metabolism at the single-cell level, with spatial and temporal resolution. In this review, we tally the currently available imaging-based technologies and explore the emerging methods of Raman and autofluorescence lifetime imaging microscopy, which hold significant potential and offer broad applications in the field of immunometabolism.

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.

Study of nitrogen heterocycles as DNA/HSA binder, topoisomerase inhibitors and toxicological safety

Four new nitrogen-containing heterocyclic derivatives (acridine, quinoline, indole, pyridine) were synthesized and their biological properties were evaluated. The compounds showed affinity for DNA and HSA, with CAIC and CAAC displaying higher binding constants (Kb) of 9.54 × 104 and 1.06 × 106, respectively. The fluorescence quenching assay (Ksv) revealed suppression values ranging from 0.34 to 0.64 × 103 M-1 for ethidium bromide (EB) and 0.1 to 0.34 × 103 M-1 for acridine orange (AO). Molecular docking confirmed the competition of the derivatives with intercalation probes at the same binding site. At 10 μM concentrations, the derivatives inhibited topoisomerase IIα activity. In the antiproliferative assays, the compounds demonstrated activity against MCF-7 and T47-D tumor cells and nonhemolytic profile. Regarding toxicity, no acute effects were observed in the embryos. However, some compounds caused enzymatic and cardiac changes, particularly the CAIC, which increased SOD activity and altered heart rate compared to the control. These findings suggest potential antitumor action of the derivatives and indicate that substituting the acridine core with different cores does not interfere with their interaction and topoisomerase inhibition. Further investigations are required to assess possible toxicological effects, including reactive oxygen species generation.

Spirulina (Arthrospira maxima) mitigates the toxicity induced by a mixture of metal and NSAID in Xenopus laevis

Cadmium (Cd) is often detected in the environment due to its wide use in industry; also, NSAIDs are one of the most consumed pharmaceuticals, particularly diclofenac (DCF). Several studies have reported the presence of both contaminants in water bodies at concentrations ranging from ng L-1 to μg L-1; in addition, they have shown that they can induce oxidative stress in aquatic species and disturb signal transduction, cell proliferation, and intercellular communication, which could lead to teratogenesis. Spirulina has been consumed as a dietary supplement; its antioxidant, anti-inflammatory, neuroprotective, and nutritional properties are well documented. This work aimed to evaluate if Spirulina reduces the damage induced by Cd and DCF mixture in Xenopus laevis at early life stages. FETAX assay was carried out: 20 fertilized oocytes were exposed to seven different treatments on triplicate, control, Cd (24.5 μg L-1), DCF (149 μg L-1), Cd + DCF, Cd+DCF+Spirulina (2 mg L-1), Cd+DCF+Spirulina (4 mg L-1), Cd+DCF+Spirulina (10 mg L-1), malformations, mortality, and growth were evaluated after 96 h, also lipid peroxidation, superoxide dismutase and catalase activity were determined after 192 h. Cd increased DCF mortality, Cd and DCF mixture increased the incidence of malformations as well as oxidative damage; on the other hand, the results obtained show that Spirulina can be used to reduce the damage caused by the mixture of Cd and DCF since it promotes growth, reduce mortality, malformations, and oxidative stress in X. laevis.

Defining roles of specific reactive oxygen species (ROS) in cell biology and physiology

'Reactive oxygen species' (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H₂O₂ and O₂^.-. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H₂O₂, O₂^.- and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O₂ levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.

Reciprocal Regulation of Shh Trafficking and H2O2 Levels via a Noncanonical BOC-Rac1 Pathway

Among molecules that bridge environment, cell metabolism, and cell signaling, hydrogen peroxide (H₂O₂) recently appeared as an emerging but central player. Its level depends on cell metabolism and environment and was recently shown to play key roles during embryogenesis, contrasting with its long-established role in disease progression. We decided to explore whether the secreted morphogen Sonic hedgehog (Shh), known to be essential in a variety of biological processes ranging from embryonic development to adult tissue homeostasis and cancers, was part of these interactions. Here, we report that H₂O₂ levels control key steps of Shh delivery in cell culture: increased levels reduce primary secretion, stimulate endocytosis and accelerate delivery to recipient cells; in addition, physiological in vivo modulation of H₂O₂ levels changes Shh distribution and tissue patterning. Moreover, a feedback loop exists in which Shh trafficking controls H₂O₂ synthesis via a non-canonical BOC-Rac1 pathway, leading to cytoneme growth. Our findings reveal that Shh directly impacts its own distribution, thus providing a molecular explanation for the robustness of morphogenesis to both environmental insults and individual variability.

Reactive oxygen species (ROS) constitute an additional player in regulating epithelial development

Reactive oxygen species (ROS) are highly reactive molecules produced in cells. So far, they have mostly been connected to diseases and pathological conditions. More recent results revealed a somewhat unexpected role of ROS in control of developmental processes. In this review, we elaborate on ROS in development, focussing on their connection to epithelial tissue morphogenesis. After briefly summarising unique characteristics of epithelial cells, we present some characteristic features of ROS species, their production and targets, with a focus on proteins important for epithelial development and function. Finally, we provide examples of regulation of epithelial morphogenesis by ROS, and also of developmental genes that regulate the overall redox status. We conclude by discussing future avenues of research that will further elucidate ROS regulation in epithelial development.

The tolerance to hypoxia is defined by a time-sensitive response of the gene regulatory network in sea urchin embryos

Deoxygenation, the reduction of oxygen level in the oceans induced by global warming and anthropogenic disturbances, is a major threat to marine life. This change in oxygen level could be especially harmful to marine embryos that use endogenous hypoxia and redox gradients as morphogens during normal development. Here, we show that the tolerance to hypoxic conditions changes between different developmental stages of the sea urchin embryo, possibly due to the structure of the gene regulatory networks (GRNs). We demonstrate that during normal development, the bone morphogenetic protein (BMP) pathway restricts the activity of the vascular endothelial growth factor (VEGF) pathway to two lateral domains and this restriction controls proper skeletal patterning. Hypoxia applied during early development strongly perturbs the activity of Nodal and BMP pathways that affect the VEGF pathway, dorsal-ventral (DV) and skeletogenic patterning. These pathways are largely unaffected by hypoxia applied after DV-axis formation. We propose that the use of redox and hypoxia as morphogens makes the sea urchin embryo highly sensitive to environmental hypoxia during early development, but the GRN structure provides higher tolerance to hypoxia at later stages.

Summary: The use of hypoxia and redox gradients as morphogens makes sea urchin early development sensitive to environmental hypoxia. This sensitivity decreases later, possibly due to the gene regulatory network structure.

ROS Live Cell Imaging During Neuronal Development

Reactive oxygen species (ROS) are well-established signaling molecules, which are important in normal development, homeostasis, and physiology. Among the different ROS, hydrogen peroxide (H2O2) is best characterized with respect to roles in cellular signaling. H2O2 has been implicated during the development in several species. For example, a transient increase in H2O2 has been detected in zebrafish embryos during the first days following fertilization. Furthermore, depleting an important cellular H2O2 source, NADPH oxidase (NOX), impairs nervous system development such as the differentiation, axonal growth, and guidance of retinal ganglion cells (RGCs) both in vivo and in vitro. Here, we describe a method for imaging intracellular H2O2 levels in cultured zebrafish neurons and whole larvae during development using the genetically encoded H2O2-specific biosensor, roGFP2-Orp1. This probe can be transiently or stably expressed in zebrafish larvae. Furthermore, the ratiometric readout diminishes the probability of detecting artifacts due to differential gene expression or volume effects. First, we demonstrate how to isolate and culture RGCs derived from zebrafish embryos that transiently express roGFP2-Orp1. Then, we use whole larvae to monitor H2O2 levels at the tissue level. The sensor has been validated by the addition of H2O2. Additionally, this methodology could be used to measure H2O2 levels in specific cell types and tissues by generating transgenic animals with tissue-specific biosensor expression. As zebrafish facilitate genetic and developmental manipulations, the approach demonstrated here could serve as a pipeline to test the role of H2O2 during neuronal and general embryonic development in vertebrates.