Redox biosensors in a context of multiparameter imaging

Affinity Peptide-Based Circularly Permuted Fluorescent Protein Biosensors for Non-Small Cell Lung Cancer Diagnosis

Non-small cell lung cancer (NSCLC) is the predominant form of lung cancer and poses a significant public health challenge. Early detection is crucial for improving patient outcomes, with serum biomarkers such as carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCCAg), and cytokeratin fragment 19 (CYFRA 21-1) playing a critical role in early screening and pathological classification of NSCLC. However, due to being mainly based on corresponding antibody binding reactions, existing detection technologies for these serum biomarkers have shortcomings such as complex operations, high false positive rates, and high costs. This study aimed to develop new methods for detecting CEA, SCCAg, and CYFRA 21-1 to assist in the diagnosis of NSCLC. Affinity peptides of CEA, SCCAg, and CYFRA 21-1, respectively, were screened by phage display technology, and the peptides' binding affinities were determined by enzyme-linked immunosorbent assay and biolayer interferometry. Peptides with high affinity were then integrated as binding domains into biosensors by fusing them with circularly permuted fluorescent proteins (cpFPs) through genetic coding. The resulting biosensors, C4 biosensor for CEA, S1 biosensor for SCCAg, and Y3 biosensor for CYFRA 21-1, demonstrated robust sensitivity and specificity even at concentrations as low as 1 ng/mL for their respective tumor markers. When applied to clinical samples and recalibrated for the upper limit of normal concentrations, the biosensors exhibited enhanced sensitivity and specificity for NSCLC diagnosis. This study introduced innovative biosensors for the detection of CEA, SCCAg, and CYFRA 21-1, providing a highly sensitive, specific, rapid, and cost-effective diagnostic alternative that could significantly improve NSCLC screening rates.

Click Coupling of Flavylium Dyes with Plasmodione Analogues: Towards New Redox-Sensitive Pro-Fluorophores

The development of redox-sensitive molecular fluorescent probes for the detection of redox changes in Plasmodium falciparum-parasitized red blood cells remains of interest due to the limitations of current genetically encoded biosensors. This study describes the design, screening and synthesis of new pro-fluorophores based on flavylium azido dyes coupled by CuAAC click chemistry to alkynyl analogues of plasmodione oxide, the key metabolite of the potent redox-active antimalarial plasmodione. The photophysical and electrochemical properties of these probes were evaluated, focusing on their fluorogenic responses. The influence of both the redox status of the quinone and the length of the PEG chain separating the fluorophore from the electrophore on the photophysical properties was investigated. The fluorescence quenching by photoinduced electron transfer is reversible and of high amplitude for probes in oxidized quinone forms and fluorescence is reinstated for reduced hydroquinone forms. Our results demonstrate that shortening the PEG chain has the effect of enhancing the fluorogenic response, likely due to non-covalent interactions between the two chromophores. All these systems were evaluated for their antiparasitic activities and fluorescence imaging suggests the efficacy of the fluorescent flavylium dyes in P. falciparum-parasitized red blood cells, paving the way for future parasite imaging studies to monitor cellular redox processes.

The centrality of redox regulation and sensing of reactive oxygen species in abiotic and biotic stress acclimatization

During land plant evolution, the number of genes encoding for components of the thiol redox regulatory network and the generator systems of reactive oxygen species (ROS) expanded, tentatively indicating that they have a role in tailored environmental acclimatization. This hypothesis has been validated both experimentally and theoretically during the last few decades. Recent developments of dynamic redox-sensitive GFP (roGFP)-based in vivo sensors for H2O2 and the redox potential of the glutathione pool have paved the way for dissecting the kinetics changes that occur in these crucial parameters in response to environmental stressors. The versatile cellular redox sensory and response regulatory system monitors alterations in redox metabolism and controls the activity of redox target proteins, and thereby affects most, if not all, cellular processes ranging from transcription to translation and metabolism. This review uses examples to describe the role of the redox- and ROS-dependent regulatory network in realising the appropriate responses to diverse environmental stresses. The selected case studies concern different environmental challenges, namely excess excitation energy, the heavy metal cadmium and the metalloid arsenic, nitrogen or phosphate shortages as examples for nutrient deficiency, wounding, and nematode infestation. Each challenge affects the redox-regulatory and ROS network, but our present state of knowledge also points toward pressing questions that remain open in relation to the translation of redox regulation to environmental acclimatization.

Genetics aspect of vitamin C (Ascorbic Acid) biosynthesis and signaling pathways in fruits and vegetables crops

Vitamin C, also known as ascorbic acid, is an essential nutrient that plays a critical role in many physiological processes in plants and animals. In humans, vitamin C is an antioxidant, reducing agent, and cofactor in diverse chemical processes. The established role of vitamin C as an antioxidant in plants is well recognized. It neutralizes reactive oxygen species (ROS) that can cause damage to cells. Also, it plays an important role in recycling other antioxidants, such as vitamin E, which helps maintain the overall balance of the plant's antioxidant system. However, unlike plants, humans cannot synthesize ascorbic acid or vitamin C in their bodies due to the absence of an enzyme called gulonolactone oxidase. This is why humans need to obtain vitamin C through their diet. Different fruits and vegetables contain varying levels of vitamin C. The biosynthesis of vitamin C in plants occurs primarily in the chloroplasts and the endoplasmic reticulum (ER). The biosynthesis of vitamin C is a complex process regulated by various factors such as light, temperature, and plant hormones. Recent research has identified several key genes that regulate vitamin C biosynthesis, including the GLDH and GLDH genes. The expression of these genes is known to be regulated by various factors such as light, temperature, and plant hormones. Recent studies highlight vitamin C's crucial role in regulating plant stress response pathways, encompassing drought, high salinity, and oxidative stress. The key enzymes in vitamin C biosynthesis are L-galactose dehydrogenase (GLDH) and L-galactono-1, 4-lactone dehydrogenase (GLDH). Genetic studies reveal key genes like GLDH and GLDH in Vitamin C biosynthesis, offering potential for crop improvement. Genetic variations influence nutritional content through their impact on vitamin C levels. Investigating the roles of genes in stress responses provides insights for developing resilient techniques in crop growth. Some fruits and vegetables, such as oranges, lemons, and grapefruits, along with strawberries and kiwi, are rich in vitamin C. Guava. Papaya provides a boost of vitamin C and dietary fiber. At the same time, red and yellow bell peppers, broccoli, pineapple, mangoes, and kale are additional sources of this essential nutrient, promoting overall health. In this review, we will discuss a brief history of Vitamin C and its signaling and biosynthesis pathway and summarize the regulation of its content in various fruits and vegetables.

Lighting the light reactions of photosynthesis by means of redox-responsive genetically encoded biosensors for photosynthetic intermediates

Oxygenic photosynthesis involves light and dark phases. In the light phase, photosynthetic electron transport provides reducing power and energy to support the carbon assimilation process. It also contributes signals to defensive, repair, and metabolic pathways critical for plant growth and survival. The redox state of components of the photosynthetic machinery and associated routes determines the extent and direction of plant responses to environmental and developmental stimuli, and therefore, their space- and time-resolved detection in planta becomes critical to understand and engineer plant metabolism. Until recently, studies in living systems have been hampered by the inadequacy of disruptive analytical methods. Genetically encoded indicators based on fluorescent proteins provide new opportunities to illuminate these important issues. We summarize here information about available biosensors designed to monitor the levels and redox state of various components of the light reactions, including NADP(H), glutathione, thioredoxin, and reactive oxygen species. Comparatively few probes have been used in plants, and their application to chloroplasts poses still additional challenges. We discuss advantages and limitations of biosensors based on different principles and propose rationales for the design of novel probes to estimate the NADP(H) and ferredoxin/flavodoxin redox poise, as examples of the exciting questions that could be addressed by further development of these tools. Genetically encoded fluorescent biosensors are remarkable tools to monitor the levels and/or redox state of components of the photosynthetic light reactions and accessory pathways. Reducing equivalents generated at the photosynthetic electron transport chain in the form of NADPH and reduced ferredoxin (FD) are used in central metabolism, regulation, and detoxification of reactive oxygen species (ROS). Redox components of these pathways whose levels and/or redox status have been imaged in plants using biosensors are highlighted in green (NADPH, glutathione, H2O2, thioredoxins). Analytes with available biosensors not tried in plants are shown in pink (NADP+). Finally, redox shuttles with no existing biosensors are circled in light blue. APX, ASC peroxidase; ASC, ascorbate; DHA, dehydroascorbate; DHAR, DHA reductase; FNR, FD-NADP+ reductase; FTR, FD-TRX reductase; GPX, glutathione peroxidase; GR, glutathione reductase; GSH, reduced glutathione; GSSG, oxidized glutathione; MDA, monodehydroascorbate; MDAR, MDA reductase; NTRC, NADPH-TRX reductase C; OAA, oxaloacetate; PRX, peroxiredoxin; PSI, photosystem I; PSII: photosystem II; SOD, superoxide dismutase; TRX, thioredoxin.

Chemogenetic approaches to dissect the role of H2O2 in redox-dependent pathways using genetically encoded biosensors

Chemogenetic tools are recombinant enzymes that can be targeted to specific organelles and tissues. The provision or removal of the enzyme substrate permits control of its biochemical activities. Yeast-derived enzyme D-amino acid oxidase (DAAO) represents the first of its kind for a substrate-based chemogenetic approach to modulate H2O2 concentrations within cells. Combining these powerful enzymes with multiparametric imaging methods exploiting genetically encoded biosensors has opened new lines of investigations in life sciences. In recent years, the chemogenetic DAAO approach has proven beneficial to establish a new role for (patho)physiological oxidative stress on redox-dependent signaling and metabolic pathways in cultured cells and animal model systems. This mini-review covers established or emerging methods and assesses newer approaches exploiting chemogenetic tools combined with genetically encoded biosensors.

Complexities of the chemogenetic toolkit: Differential mDAAO activation by d-amino substrates and subcellular targeting

A common approach to investigate oxidant-regulated intracellular pathways is to add exogenous H2O2 to living cells or tissues. However, the addition of H2O2 to the culture medium of cells or tissues approach does not accurately replicate intracellular redox-mediated cell responses. d-amino acid oxidase (DAAO)-based chemogenetic tools represent informative methodological advances that permit the generation of H2O2 on demand with a high spatiotemporal resolution by providing or withdrawing the DAAO substrate d-amino acids. Much has been learned about the intracellular transport of H2O2 through studies using DAAO, yet these valuable tools remain incompletely characterized in many cultured cells. In this study, we describe and characterize in detail the features of a new modified variant of DAAO (termed mDAAO) with improved catalytic activities. We tested mDAAO functionality in several cultured cell lines employing live-cell imaging techniques. Our imaging experiments show that mDAAO is suitable for the generation of H2O2 under hypoxic conditions imaged with the novel ultrasensitive H2O2 sensor (HyPer7). Moreover, this approach was suitable for generating H2O2 in a reversible and concentration-dependent manner in subcellular locales. Furthermore, we show that the choice of d-amino acids differentially affects mDAAO-dependent intracellular H2O2 generation. When paired with the hydrogen sulfide (H2S) sensor hsGFP, administration of the sulfur-containing amino acid d-cysteine to cells expressing mDAAO generates robust H2S signals. We also show that chemogenetic H2O2 generation in different cell types yields distinct HyPer7 profiles. These studies fully characterize the new mDAAO as a novel chemogenetic tool and provide multiparametric approaches for cell manipulation that may open new lines of investigations for redox biochemists to dissect the role of ROS signaling pathways with high spatial and temporal precision.

A Co-Culture-Based Multiparametric Imaging Technique to Dissect Local H2O2 Signals with Targeted HyPer7

Multispectral live-cell imaging is an informative approach that permits detecting biological processes simultaneously in the spatial and temporal domain by exploiting spectrally distinct biosensors. However, the combination of fluorescent biosensors with distinct spectral properties such as different sensitivities, and dynamic ranges can undermine accurate co-imaging of the same analyte in different subcellular locales. We advanced a single-color multiparametric imaging method, which allows simultaneous detection of hydrogen peroxide (H2O2) in multiple cell locales (nucleus, cytosol, mitochondria) using the H2O2 biosensor HyPer7. Co-culturing of endothelial cells stably expressing differentially targeted HyPer7 biosensors paved the way for co-imaging compartmentalized H2O2 signals simultaneously in neighboring cells in a single experimental setup. We termed this approach COMPARE IT, which is an acronym for co-culture-based multiparametric imaging technique. Employing this approach, we detected lower H2O2 levels in mitochondria of endothelial cells compared to the cell nucleus and cytosol under basal conditions. Upon administering exogenous H2O2, the cytosolic and nuclear-targeted probes displayed similarly slow and moderate HyPer7 responses, whereas the mitochondria-targeted HyPer7 signal plateaued faster and reached higher amplitudes. Our results indicate striking differences in mitochondrial H2O2 accumulation of endothelial cells. Here, we present the method's potential as a practicable and informative multiparametric live-cell imaging technique.

A guide to genetically encoded tools for the study of H2 O2

Cell metabolism heavily relies on the redox reactions that inevitably generate reactive oxygen species (ROS). It is now well established that ROS fluctuations near basal levels coordinate numerous physiological processes in living organisms, thus exhibiting regulatory functions. Hydrogen peroxide, the most long-lived ROS, is a key contributor to ROS-dependent signal transduction in the cell. H₂ O₂ is known to impact various targets in the cell; therefore, the question of how H₂ O₂ modulates physiological processes in a highly specific manner is central in redox biology. To resolve this question, novel genetic tools have recently been created for detecting H₂ O₂ and emulating its generation in living organisms with unmatched spatiotemporal resolution. Here, we review H₂ O₂ -sensitive genetically encoded fluorescent sensors and opto- and chemogenetic tools for controlled H₂ O₂ generation.

Live monitoring of plant redox and energy physiology with genetically encoded biosensors

Genetically encoded biosensors pave the way for understanding plant redox dynamics and energy metabolism on cellular and subcellular levels.

In Vivo Imaging with Genetically Encoded Redox Biosensors

Redox reactions are of high fundamental and practical interest since they are involved in both normal physiology and the pathogenesis of various diseases. However, this area of research has always been a relatively problematic field in the context of analytical approaches, mostly because of the unstable nature of the compounds that are measured. Genetically encoded sensors allow for the registration of highly reactive molecules in real-time mode and, therefore, they began a new era in redox biology. Their strongest points manifest most brightly in in vivo experiments and pave the way for the non-invasive investigation of biochemical pathways that proceed in organisms from different systematic groups. In the first part of the review, we briefly describe the redox sensors that were used in vivo as well as summarize the model systems to which they were applied. Next, we thoroughly discuss the biological results obtained in these studies in regard to animals, plants, as well as unicellular eukaryotes and prokaryotes. We hope that this work reflects the amazing power of this technology and can serve as a useful guide for biologists and chemists who work in the field of redox processes.

Mitochondrial Superoxide Production Decreases on Glucose-Stimulated Insulin Secretion in Pancreatic β Cells Due to Decreasing Mitochondrial Matrix NADH/NAD+ Ratio

Aims: Glucose-stimulated insulin secretion (GSIS) in pancreatic β cells was expected to enhance mitochondrial superoxide formation. Hence, we elucidated relevant redox equilibria. Results: Unexpectedly, INS-1E cells at transitions from 3 (11 mM; pancreatic islets from 5 mM) to 25 mM glucose decreased matrix superoxide release rates (MitoSOX Red monitoring validated by MitoB) and H2O2 (mitoHyPer, subtracting mitoSypHer emission). Novel double-channel fluorescence lifetime imaging, approximating free mitochondrial matrix NADHF, indicated its ∼20% decrease. Matrix NAD+F increased on GSIS, indicated by the FAD-emission lifetime decrease, reflecting higher quenching of FAD by NAD+F. The participation of pyruvate/malate and pyruvate/citrate redox shuttles, elevating cytosolic NADPHF (iNAP1 fluorescence monitoring) at the expense of matrix NADHF, was indicated, using citrate (2-oxoglutarate) carrier inhibitors and cytosolic malic enzyme silencing: All changes vanished on these manipulations. 13C-incorporation from 13C-L-glutamine into 13C-citrate reflected the pyruvate/isocitrate shuttle. Matrix NADPHF (iNAP3 monitored) decreased. With decreasing glucose, the suppressor of Complex III site Q electron leak (S3QEL) suppressor caused a higher Complex I IF site contribution, but a lower superoxide fraction ascribed to the Complex III site IIIQo. Thus, the diminished matrix NADHF/NAD+F decreased Complex I flavin site IF superoxide formation on GSIS. Innovation: Mutually validated methods showed decreasing superoxide release into the mitochondrial matrix in pancreatic β cells on GSIS, due to the decreasing matrix NADHF/NAD+F (NADPHF/NADP+F) at increasing cytosolic NADPHF levels. The developed innovative methods enable real-time NADH/NAD+ and NADPH/NADP+ monitoring in any distinct cell compartment. Conclusion: The export of reducing equivalents from mitochondria adjusts lower mitochondrial superoxide production on GSIS, but it does not prevent oxidative stress in pancreatic β cells.

Genetically Encoded Tools for Research of Cell Signaling and Metabolism under Brain Hypoxia

Hypoxia is characterized by low oxygen content in the tissues. The central nervous system (CNS) is highly vulnerable to a lack of oxygen. Prolonged hypoxia leads to the death of brain cells, which underlies the development of many pathological conditions. Despite the relevance of the topic, different approaches used to study the molecular mechanisms of hypoxia have many limitations. One promising lead is the use of various genetically encoded tools that allow for the observation of intracellular parameters in living systems. In the first part of this review, we provide the classification of oxygen/hypoxia reporters as well as describe other genetically encoded reporters for various metabolic and redox parameters that could be implemented in hypoxia studies. In the second part, we discuss the advantages and disadvantages of the primary hypoxia model systems and highlight inspiring examples of research in which these experimental settings were combined with genetically encoded reporters.

High-throughput screening in multicellular spheroids for target discovery in the tumor microenvironment

INTRODUCTION

Solid tumors are highly influenced by a complex tumor microenvironment (TME) that cannot be modeled with conventional two-dimensional (2D) cell culture. In addition, monolayer culture conditions tend to induce undesirable molecular and phenotypic cellular changes. The discrepancy between in vitro and in vivo is an important factor accounting for the high failure rate in drug development. Three-dimensional (3D) multicellular tumor spheroids (MTS) more closely resemble the in vivo situation in avascularized tumors.

AREAS COVERED

This review describes the use of MTS for anti-cancer drug discovery, with an emphasis on high-throughput screening (HTS) compatible assays. In particular, we focus on how these assays can be used for target discovery in the context of the TME.

EXPERT OPINION

Arrayed MTS in microtiter plates are HTS compatible but remain more expensive and time consuming than their 2D culture counterpart. It is therefore imperative to use assays with multiplexed readouts, in order to maximize the information that can be gained with the screen. In this context, high-content screening allowing to uncover microenvironmental dependencies is the true added value of MTS-based screening compared to 2D culture-based screening. Hit translation in animal models will, however, be key to allow a broader use of MTS-based screening in industry.

Circularly Permuted Fluorescent Protein-Based Indicators: History, Principles, and Classification

Genetically encoded biosensors based on fluorescent proteins (FPs) are a reliable tool for studying the various biological processes in living systems. The circular permutation of single FPs led to the development of an extensive class of biosensors that allow the monitoring of many intracellular events. In circularly permuted FPs (cpFPs), the original N- and C-termini are fused using a peptide linker, while new termini are formed near the chromophore. Such a structure imparts greater mobility to the FP than that of the native variant, allowing greater lability of the spectral characteristics. One of the common principles of creating genetically encoded biosensors is based on the integration of a cpFP into a flexible region of a sensory domain or between two interacting domains, which are selected according to certain characteristics. Conformational rearrangements of the sensory domain associated with ligand interaction or changes in the cellular parameter are transferred to the cpFP, changing the chromophore environment. In this review, we highlight the basic principles of such sensors, the history of their creation, and a complete classification of the available biosensors.

Measuring intracellular concentration of hydrogen peroxide with the use of genetically encoded H2O2 biosensor HyPer

In this study, we propose a method for quantification of average hydrogen peroxide concentration within a living cell that is based on the use of genetically encoded H₂O₂ biosensor HyPer. The method utilizes flow cytometric measurements of HyPer fluorescence in H₂O₂-exposed cells to analyze the biosensor oxidation kinetics. Fitting the experimental curves with kinetic equations allows determining the rate constants of HyPer oxidation/reduction which are used further for the calculation of peroxide concentrations in the cells of interest both in the presence and absence of external H₂O₂. Applying this method to K562 cells, we have estimated the gradient as about 390-fold between the extracellular and intracellular level of exogenous H₂O₂ in cells exposed to the micromole doses of peroxide, as well as the average basal level of H₂O₂ in the cytosol of undisturbed cells ([H2O2]basal=2.2±0.4nM). The method can be extended to other H₂O₂-sensitive redox probes or to procedures in which, rather than adding external peroxide, intracellular production of peroxide is triggered, providing a tool to quantitate not only basal average H₂O₂ concentrations but also the concentration of peroxide build up in the vicinity of redox probes.

A genetically encoded biosensor roKate for monitoring the redox state of the glutathione pool

Genetically encoded fluorescent sensors are exploited to study a variety of biological processes in living organisms in real time. In recent years, a whole family of biosensors has been developed, serving to visualize changes in the glutathione redox state. The aim of our experiment was to design a biosensor based on the red fluorescent protein mKate2 for measuring the 2GSH/GSSG ratio. A pair of cysteine amino acid residues were introduced into the structure of the fluorescent protein using site-directed mutagenesis. These residues form a disulfide bridge when the surrounding glutathione pool is oxidized, affecting the spectral characteristics of the protein. Our biosensor, which we called roKate, was tested in vitro on an isolated protein. Specifically, we examined the spectral characteristics, pH and the redox potential of the sensor. Additionally, the performance of roKate was evaluated using the culture of living mammalian cells. The fluorescent signal emitted by the sensor was very bright and remarkably stable under pH conditions varying in the physiological range. Irreversibly oxidized in mammalian cells, roKate stands out from other members of this biosensor family. This biosensor should be preferred in the experiments when the time between the manipulations with the biological object and the subsequent analysis of the induced effect is substantial, as is the case with long sample preparation.

O2 affects mitochondrial functionality ex vivo

Mitochondria have originated in eukaryotic cells by endosymbiosis of a specialized prokaryote approximately 2 billion years ago. They are essential for normal cell function by providing energy through their role in oxidizing carbon substrates. Glutathione (GSH) is a major thiol-disulfide redox buffer of the cell including the mitochondrial matrix and intermembrane space. We have generated cardiomyocyte-specific Grx1-roGFP2 GSH redox potential (E_GSH) biosensor mice in the past, in which the sensor is targeted to the mitochondrial matrix. Using this mouse model a distinct E_GSH of the mitochondrial matrix (−278.9 ± 0.4 mV) in isolated cardiomyocytes is observed. When analyzing the E_GSH in isolated mitochondria from the transgenic hearts, however, the E_GSH in the mitochondrial matrix is significantly oxidized (−247.7 ± 8.7 mV). This is prevented by adding N-Ethylmaleimide during the mitochondria isolation procedure, which precludes disulfide bond formation. A similar reducing effect is observed by isolating mitochondria in hypoxic (0.1–3% O₂) conditions that mimics mitochondrial pO₂ levels in cellulo. The reduced E_GSH is accompanied by lower ROS production, reduced complex III activity but increased ATP levels produced at baseline and after stimulation with succinate/ADP. Altogether, we demonstrate that oxygenation is an essential factor that needs to be considered when analyzing mitochondrial function ex vivo.

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We identified that mitochondria isolated in room air at 20.9% O₂ exhibit a strong oxidation of the E_GSH in the matrix.

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Isolation of mitochondria in hypoxic conditions mimicking their in cellulo conditions prevents oxidation of the E_GSH.

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Normoxic and hypoxic isolated mitochondria differ in ROS production, complex III activity and ATP levels.

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Oxygenation needs to be considered when analyzing mitochondrial function ex vivo.

Red fluorescent redox-sensitive biosensor Grx1-roCherry

Redox-sensitive fluorescent proteins (roFPs) are a powerful tool for imaging intracellular redox changes. The structure of these proteins contains a pair of cysteines capable of forming a disulfide upon oxidation that affects the protein conformation and spectral characteristics. To date, a palette of such biosensors covers the spectral range from blue to red. However, most of the roFPs suffer from either poor brightness or high pH-dependency, or both. Moreover, there is no roRFP with the redox potential close to that of 2GSH/GSSG redox pair. In the present work, we describe Grx1-roCherry, the first red roFP with canonical FP topology and fluorescent excitation/emission spectra of typical RFP. Grx1-roCherry, with a midpoint redox potential of − 311 mV, is characterized by high brightness and increased pH stability (pKa 6.7). We successfully used Grx1-roCherry in combination with other biosensors in a multiparameter imaging mode to demonstrate redox changes in cells under various metabolic perturbations, including hypoxia/reoxygenation. In particular, using simultaneous expression of Grx1-roCherry and its green analog in various compartments of living cells, we demonstrated that local H₂O₂ production leads to compartment-specific and cell-type-specific changes in the 2GSH/GSSG ratio. Finally, we demonstrate the utility of Grx1-roCherry for in vivo redox imaging.

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We developed Grx1-roCherry, a novel redox-sensitive probe based on red FP.

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Grx1-roCherry is suitable for imaging in combination with other redox biosensors.

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Hypoxia/reoxygenation mostly affects redox state of mitochondrial GSH pool.

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Switch from glycolysis to ox.phosphorylation induces redox changes in HeLa Kyoto cells.

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Local H₂O₂ generation leads to compartment- and cell-type-specific redox changes.