Nox NADPH oxidases and the endoplasmic reticulum

Endothelial protein disulfide isomerase A1 enhances membrane stiffness and platelet-endothelium interaction in hyperglycemia via SLC3A2 and LAMC1

BACKGROUND

Diabetes carries an increased risk of cardiovascular disease and thromboembolic events. Upon endothelial dysfunction, platelets bind to endothelial cells to precipitate thrombus formation; however, it is unclear which surface proteins regulate platelet-endothelium interaction. We and others have shown that peri/epicellular protein disulfide isomerase A1 (pecPDI) influences the adhesion and migration of vascular cells.

OBJECTIVES

We investigated whether pecPDI regulates adhesion-related molecules on the surface of endothelial cells and platelets that influence the binding of these cells in hyperglycemia.

METHODS

Immunofluorescence was used to assess platelet-endothelium interaction in vitro, cytoskeleton reorganization, and focal adhesions. Hydrogen peroxide production was assessed via Amplex Red assays (ThermoFisher Scientific). Cell biophysics was assessed using atomic force microscopy. Secreted proteins of interest were identified through proteomics (secretomics), and targets were knocked down using small interfering RNA. Protein disulfide isomerase A1 (PDI) contribution was assessed using whole-cell PDI or pecPDI inhibitors or small interfering RNA.

RESULTS

Platelets of healthy donors adhered more onto hyperglycemic human umbilical vein endothelial cells (HUVECs). Endothelial, but not platelet, pecPDI regulated this effect. Hyperglycemic HUVECs showed marked cytoskeleton reorganization, increased H2O2 production, and elongated focal adhesions. Indeed, hyperglycemic HUVECs were stiffer compared with normoglycemic cells. PDI and pecPDI inhibition reversed the abovementioned processes in hyperglycemic cells. A secretomics analysis revealed 8 proteins secreted in a PDI-dependent manner by hyperglycemic cells. Among these, we showed that genetic deletion of LAMC1 and SLC3A2 decreased platelet-endothelium interaction and did not potentiate the effects of PDI inhibitors.

CONCLUSION

Endothelial pecPDI regulates platelet-endothelium interaction in hyperglycemia through adhesion-related proteins and alterations in endothelial membrane biophysics.

Peroxiporins and Oxidative Stress: Promising Targets to Tackle Inflammation and Cancer

Peroxiporins are a specialized subset of aquaporins, which are integral membrane proteins primarily known for facilitating water transport across cell membranes. In addition to the classical water transport function, peroxiporins have the unique capability to transport hydrogen peroxide (H2O2), a reactive oxygen species involved in various cellular signaling pathways and regulation of oxidative stress responses. The regulation of H2O2 levels is crucial for maintaining cellular homeostasis, and peroxiporins play a significant role in this process by modulating its intracellular and extracellular concentrations. This ability to facilitate the passage of H2O2 positions peroxiporins as key players in redox biology and cellular signaling, with implications for understanding and treating various diseases linked to oxidative stress and inflammation. This review provides updated information on the physiological roles of peroxiporins and their implications in disease, emphasizing their potential as novel biomarkers and drug targets in conditions where they are dysregulated, such as inflammation and cancer.

Functionality of Reactive Oxygen Species (ROS) in Plants: Toxicity and Control in Poaceae Crops Exposed to Abiotic Stress

Agriculture and changing environmental conditions are closely related, as weather changes could adversely affect living organisms or regions of crop cultivation. Changing environmental conditions trigger different abiotic stresses, which ultimately cause the accumulation of reactive oxygen species (ROS) in plants. Common ROS production sites are the chloroplast, endoplasmic reticulum, plasma membrane, mitochondria, peroxisomes, etc. The imbalance in ROS production and ROS detoxification in plant cells leads to oxidative damage to biomolecules such as lipids, nucleic acids, and proteins. At low concentrations, ROS initiates signaling events related to development and adaptations to abiotic stress in plants by inducing signal transduction pathways. In plants, a stress signal is perceived by various receptors that induce a signal transduction pathway that activates numerous signaling networks, which disrupt gene expression, impair the diversity of kinase/phosphatase signaling cascades that manage the stress response in the plant, and result in changes in physiological responses under various stresses. ROS production also regulates ABA-dependent and ABA-independent pathways to mitigate drought stress. This review focuses on the common subcellular location of manufacturing, complex signaling mechanisms, and networks of ROS, with an emphasis on cellular effects and enzymatic and non-enzymatic antioxidant scavenging mechanisms of ROS in Poaceae crops against drought stress and how the manipulation of ROS regulates stress tolerance in plants. Understanding ROS systems in plants could help to create innovative strategies to evolve paths of cell protection against the negative effects of excessive ROS in attempts to improve crop productivity in adverse environments.

Dissecting the pleiotropic roles of reactive oxygen species (ROS) in lung cancer: From carcinogenesis toward therapy

Lung cancer is a major cause of morbidity and mortality. The specific pulmonary structure to directly connect with ambient air makes it more susceptible to damage from airborne toxins. External oxidative stimuli and endogenous reactive oxygen species (ROS) play a crucial role in promoting lung carcinogenesis and development. The biological properties of higher ROS levels in tumor cells than in normal cells make them more sensitive and vulnerable to ROS injury. Therefore, the strategy of targeting ROS has been proposed for cancer therapy for decades. However, it is embarrassing that countless attempts at ROS-based therapies have had very limited success, and no FDA approval in the anticancer list was mechanistically based on ROS manipulation. Even compared with the untargetable proteins, such as transcription factors, ROS are more difficult to be targeted due to their chemical properties. Thus, the pleiotropic roles of ROS provide therapeutic potential for anticancer drug discovery, while a better dissection of the mechanistic action and signaling pathways is a prerequisite for future breakthroughs. This review discusses the critical roles of ROS in cancer carcinogenesis, ROS-inspired signaling pathways, and ROS-based treatment, exemplified by lung cancer. In particular, an eight considerations rule is proposed for ROS-targeting strategies and drug design and development.

Modulation of neuroinflammation and oxidative stress by targeting GPR55 - new approaches in the treatment of psychiatric disorders

Pharmacological treatment of psychiatric disorders remains challenging in clinical, pharmacological, and scientific practice. Even if many different substances are established for treating different psychiatric conditions, subgroups of patients show only small or no response to the treatment. The neuroinflammatory hypothesis of the genesis of psychiatric disorders might explain underlying mechanisms in these non-responders. For that reason, recent research focus on neuroinflammatory processes and oxidative stress as possible causes of psychiatric disorders. G-protein coupled receptors (GPCRs) form the biggest superfamily of membrane-bound receptors and are already well known as pharmacological targets in various diseases. The G-protein coupled receptor 55 (GPR55), a receptor considered part of the endocannabinoid system, reveals promising modulation of neuroinflammatory and oxidative processes. Different agonists and antagonists reduce pro-inflammatory cytokine release, enhance the synthesis of anti-inflammatory mediators, and protect cells from oxidative damage. For this reason, GPR55 ligands might be promising compounds in treating subgroups of patients suffering from psychiatric disorders related to neuroinflammation or oxidative stress. New approaches in drug design might lead to new compounds targeting different pathomechanisms of those disorders in just one molecule.

Disturbed flow regulates protein disulfide isomerase A1 expression via microRNA-204

Redox processes can modulate vascular pathophysiology. The endoplasmic reticulum redox chaperone protein disulfide isomerase A1 (PDIA1) is overexpressed during vascular proliferative diseases, regulating thrombus formation, endoplasmic reticulum stress adaptation, and structural remodeling. However, both protective and deleterious vascular effects have been reported for PDIA1, depending on the cell type and underlying vascular condition. Further understanding of this question is hampered by the poorly studied mechanisms underlying PDIA1 expression regulation. Here, we showed that PDIA1 mRNA and protein levels were upregulated (average 5-fold) in the intima and media/adventitia following partial carotid ligation (PCL). Our search identified that miR-204-5p and miR-211-5p (miR-204/211), two broadly conserved miRNAs, share PDIA1 as a potential target. MiR-204/211 was downregulated in vascular layers following PCL. In isolated endothelial cells, gain-of-function experiments of miR-204 with miR mimic decreased PDIA1 mRNA while having negligible effects on markers of endothelial activation/stress response. Similar effects were observed in vascular smooth muscle cells (VSMCs). Furthermore, PDIA1 downregulation by miR-204 decreased levels of the VSMC contractile differentiation markers. In addition, PDIA1 overexpression prevented VSMC dedifferentiation by miR-204. Collectively, we report a new mechanism for PDIA1 regulation through miR-204 and identify its relevance in a model of vascular disease playing a role in VSMC differentiation. This mechanism may be regulated in distinct stages of atherosclerosis and provide a potential therapeutic target.

Placental cartography of NADPH oxidase (NOX) family proteins: Involvement in the pathophysiology of preeclampsia

The placenta is an essential organ for fetal development. During the first trimester, it undergoes dramatic changes as it develops in an environment poor in oxygen (around 2-3%). From about 10 gestational weeks, oxygen levels increase to 8% in the intervillous chamber. These changes are accompanied by modulation of the activity of NADPH oxidase, a major source of production of reactive oxygen species in the first trimester of pregnancy. The NOX complex is composed of seven different proteins (NOX1-5 and DUOX1-2) whose placental involvements during physiological and pathological pregnancies are largely unknown. The aim of the study was to produce a cartography of NOX family proteins, in terms of RNA, protein expression, and localization during physiological pregnancy and in the case of preeclampsia (PE), in a cohort of early-onset PE (n = 11) and late-onset PE (n = 7) cases. NOX family proteins were mainly expressed in trophoblastic cells (NOX4-5, DUOX1) and modulated during physiological pregnancy. NOX4 underwent an unexpected and hitherto unreported nuclear translocation at term. In the case of PE, two groups stood out: NOX1-3, superoxide producers, were down-regulated (p < 0.05) while NOX4-DUOX1, hydrogen peroxide producers, were up-regulated (p < 0.05), compared to the control group. Mapping of placental NOX will constitute a reference and guide for future investigations concerning its involvement in the pathophysiology of PE.

Marchf6 E3 ubiquitin ligase critically regulates endoplasmic reticulum stress, ferroptosis, and metabolic homeostasis in POMC neurons

The metabolic prohormone pro-opiomelanocortin (POMC) is generally translocated into the endoplasmic reticulum (ER) for entry into the secretory pathway. Patients with mutations within the signal peptide (SP) of POMC or its adjoining segment develop metabolic disorders. However, the existence, metabolic fate, and functional outcomes of cytosol-retained POMC remain unclear. Here, we show that SP-uncleaved POMC is produced in the cytosol of POMC neuronal cells, thus inducing ER stress and ferroptotic cell death. Mechanistically, the cytosol-retained POMC sequesters the chaperone Hspa5 and subsequently accelerates degradation of the glutathione peroxidase Gpx4, a core regulator of ferroptosis, via the chaperone-mediated autophagy. We also show that the Marchf6 E3 ubiquitin ligase mediates the degradation of cytosol-retained POMC, thereby preventing ER stress and ferroptosis. Furthermore, POMC-Cre-mediated Marchf6-deficient mice exhibit hyperphagia, reduced energy expenditure, and weight gain. These findings suggest that Marchf6 is a critical regulator of ER stress, ferroptosis, and metabolic homeostasis in POMC neurons.

Mitochondrial cholesterol: Metabolism and impact on redox biology and disease

Cholesterol is a crucial component of membrane bilayers by regulating their structural and functional properties. Cholesterol traffics to different cellular compartments including mitochondria, whose cholesterol content is low compared to other cell membranes. Despite the limited availability of cholesterol in the inner mitochondrial membrane (IMM), the metabolism of cholesterol in the IMM plays important physiological roles, acting as the precursor for the synthesis of steroid hormones and neurosteroids in steroidogenic tissues and specific neurons, respectively, or the synthesis of bile acids through an alternative pathway in the liver. Accumulation of cholesterol in mitochondria above physiological levels has a negative impact on mitochondrial function through several mechanisms, including the limitation of crucial antioxidant defenses, such as the glutathione redox cycle, increased generation of reactive oxygen species and consequent oxidative modification of cardiolipin, and defective assembly of respiratory supercomplexes. These adverse consequences of increased mitochondrial cholesterol trafficking trigger the onset of oxidative stress and cell death, and, ultimately, contribute to the development of diverse diseases, including metabolic liver diseases (i.e. fatty liver disease and liver cancer), as well as lysosomal disorders (i.e. Niemann-Pick type C disease) and neurodegenerative diseases (i.e. Alzheimer's disease). In this review, we summarize the metabolism and regulation of mitochondrial cholesterol and its potential impact on liver and neurodegenerative diseases.

Targeting M2 Macrophages with a Novel NADPH Oxidase Inhibitor

ROS in cancer cells play a key role in pathways regulating cell death, stemness maintenance, and metabolic reprogramming, all of which have been implicated in resistance to chemo/ immunotherapy. Adjusting ROS levels to reverse the resistance of cancer cells without impairing normal cell functions is a new therapeutic avenue. In this paper, we describe new inhibitors of NADPH oxidase (NOX), a key enzyme in many cells of the tumor microenvironment. The first inhibitor, called Nanoshutter-1, NS1, decreased the level of tumor-promoting "M2" macrophages differentiated from human blood monocytes. NS1 disrupted the active NADPH oxidase-2 (NOX2) complex at the membrane and in the mitochondria of the macrophages, as shown by confocal microscopy. As one of the characteristics of tumor invasion is hypoxia, we tested whether NS1 would affect vascular reactivity by reducing ROS or NO levels in wire and pressure myograph experiments on isolated blood vessels. The results show that NS1 vasodilated blood vessels and would likely reduce hypoxia. Finally, as both NOX2 and NOX4 are key proteins in tumors and their microenvironment, we investigated whether NS1 would probe these proteins differently. Models of NOX2 and NOX4 were generated by homology modeling, showing structural differences at their C-terminal NADPH site, in particular in their last Phe. Thus, the NADPH site presents an unexploited chemical space for addressing ligand specificity, which we exploited to design a novel NOX2-specific inhibitor targeting variable NOX2 residues. With the proper smart vehicle to target specific cells of the microenvironment as TAMs, NOX2-specific inhibitors could open the way to new precision therapies.

Protective Effects of Carnosol on Renal Interstitial Fibrosis in a Murine Model of Unilateral Ureteral Obstruction

Renal fibrosis is a common feature of chronic kidney disease and is a promising therapeutic target. However, there is still limited treatment for renal fibrosis, so the development of new anti-fibrotic agents is urgently needed. Accumulating evidence suggest that oxidative stress and endoplasmic reticulum (ER) stress play a critical role in renal fibrosis. Carnosol (CS) is a bioactive diterpene compound present in rosemary plants and has potent antioxidant and anti-inflammatory properties. In this study, we investigated the potential effects of CS on renal injury and fibrosis in a murine model of unilateral ureteral obstruction (UUO). Male C57BL/6J mice underwent sham or UUO surgery and received intraperitoneal injections of CS (50 mg/kg) daily for 8 consecutive days. CS improved renal function and ameliorated renal tubular injury and interstitial fibrosis in UUO mice. It suppressed oxidative injury by inhibiting pro-oxidant enzymes and activating antioxidant enzymes. Activation of ER stress was also attenuated by CS. In addition, CS inhibited apoptotic and necroptotic cell death in kidneys of UUO mice. Furthermore, cytokine production and immune cell infiltration were alleviated by CS. Taken together, these findings indicate that CS can attenuate renal injury and fibrosis in the UUO model.

Molecular Regulation and Evolution of Redox Homeostasis in Photosynthetic Machinery

The recent advances in plant biology have significantly improved our understanding of reactive oxygen species (ROS) as signaling molecules in the redox regulation of complex cellular processes. In plants, free radicals and non-radicals are prevalent intra- and inter-cellular ROS, catalyzing complex metabolic processes such as photosynthesis. Photosynthesis homeostasis is maintained by thiol-based systems and antioxidative enzymes, which belong to some of the evolutionarily conserved protein families. The molecular and biological functions of redox regulation in photosynthesis are usually to balance the electron transport chain, photosystem II, photosystem I, mesophyll and bundle sheath signaling, and photo-protection regulating plant growth and productivity. Here, we review the recent progress of ROS signaling in photosynthesis. We present a comprehensive comparative bioinformatic analysis of redox regulation in evolutionary distinct photosynthetic cells. Gene expression, phylogenies, sequence alignments, and 3D protein structures in representative algal and plant species revealed conserved key features including functional domains catalyzing oxidation and reduction reactions. We then discuss the antioxidant-related ROS signaling and important pathways for achieving homeostasis of photosynthesis. Finally, we highlight the importance of plant responses to stress cues and genetic manipulation of disturbed redox status for balanced and enhanced photosynthetic efficiency and plant productivity.

Metabolic reprogramming and alteration of the redox state in hyper-productive MDCK cells for influenza a virus production

Influenza is a global public health issue leading to widespread morbidity and mortality with devastating economic loss annually. Madin-Darby Canine Kidney (MDCK) cell line has been a major cell line for influenza vaccine applications. Though many details of the host metabolic responses upon influenza A virus (IAV) infection have been documented, little is known about the metabolic reprogramming features of a hyper-productive host for IAV vaccine production. In this study, a MDCK cell clone H1 was shown to have a particular high productivity of 30 × 10³ virions/cell. The glucose and amino acid metabolism of H1 were evaluated, indicating that the high producer had a particular metabolic reprogramming phenotype compared to its parental cell line (P): elevated glucose uptake, superior tricarboxylic acid cycle flux, moderate amino acid consumption, and better regulation of reactive oxygen species. Combined with the stronger mitochondrial function and mild antiviral and inflammatory responses characterized previously, our results indicated that the high producer had a sufficient intracellular energy supply, and balanced substrate distribution for IAV and host protein synthesis as well as the intracellular redox status. Understanding of these metabolic alterations paves the way for the rational cell line development and reasonable process optimization for high-yield influenza vaccine production.

SILAC-based quantitative proteomics to investigate the eicosanoid associated inflammatory response in activated macrophages

BACKGROUND

Macrophages play a central role in inflammation by phagocytosing invading pathogens, apoptotic cells and debris, as well as mediating repair of tissues damaged by trauma. In order to do this, these dynamic cells generate a variety of inflammatory mediators including eicosanoids such as prostaglandins, leukotrienes and hydroxyeicosatraenoic acids (HETEs) that are formed through the cyclooxygenase, lipoxygenase and cytochrome P450 pathways. The ability to examine the effects of eicosanoid production at the protein level is therefore critical to understanding the mechanisms associated with macrophage activation.

RESULTS

This study presents a stable isotope labelling with amino acids in cell culture (SILAC) -based proteomics strategy to quantify the changes in macrophage protein abundance following inflammatory stimulation with Kdo2-lipid A and ATP, with a focus on eicosanoid metabolism and regulation. Detailed gene ontology analysis, at the protein level, revealed several key pathways with a decrease in expression in response to macrophage activation, which included a promotion of macrophage polarisation and dynamic changes to energy requirements, transcription and translation. These findings suggest that, whilst there is evidence for the induction of a pro-inflammatory response in the form of prostaglandin secretion, there is also metabolic reprogramming along with a change in cell polarisation towards a reduced pro-inflammatory phenotype.

CONCLUSIONS

Advanced quantitative proteomics in conjunction with functional pathway network analysis is a useful tool to investigate the molecular pathways involved in inflammation.

Transfer of H2O2 from Mitochondria to the endoplasmic reticulum via Aquaporin-11

Some aquaporins (AQPs) can transport H2O2 across membranes, allowing redox signals to proceed in and between cells. Unlike other peroxiporins, human AQP11 is an endoplasmic reticulum (ER)-resident that can conduit H2O2 to the cytosol. Here, we show that silencing Ero1α, an ER flavoenzyme that generates abundant H2O2 during oxidative folding, causes a paradoxical increase in luminal H2O2 levels. The simultaneous AQP11 downregulation prevents this increase, implying that H2O2 reaches the ER from an external source(s). Pharmacological inhibition of the electron transport chain reveals that Ero1α downregulation activates superoxide production by complex III. In the intermembrane space, superoxide dismutase 1 generates H2O2 that enters the ER channeled by AQP11. Meanwhile, the number of ER-mitochondria contact sites increases as well, irrespective of AQP11 expression. Taken together, our findings identify a novel interorganellar redox response that is activated upon Ero1α downregulation and transfers H2O2 from mitochondria to the ER via AQP11.

Coordinated NADPH oxidase/hydrogen peroxide functions regulate cutaneous sensory axon de- and regeneration

Tissue wounding induces cutaneous sensory axon regeneration via hydrogen peroxide (H2O2) that is produced by the epithelial NADPH oxidase, Duox1. Sciatic nerve injury instead induces axon regeneration through neuronal uptake of the NADPH oxidase, Nox2, from macrophages. We therefore reasoned that the tissue environment in which axons are damaged stimulates distinct regenerative mechanisms. Here, we show that cutaneous axon regeneration induced by tissue wounding depends on both neuronal and keratinocyte-specific mechanisms involving H2O2 signaling. Genetic depletion of H2O2 in sensory neurons abolishes axon regeneration, whereas keratinocyte-specific H2O2 depletion promotes axonal repulsion, a phenotype mirrored in duox1 mutants. Intriguingly, cyba mutants, deficient in the essential Nox subunit, p22Phox, retain limited axon regenerative capacity but display delayed Wallerian degeneration and axonal fusion, observed so far only in invertebrates. We further show that keratinocyte-specific oxidation of the epidermal growth factor receptor (EGFR) at a conserved cysteine thiol (C797) serves as an attractive cue for regenerating axons, leading to EGFR-dependent localized epidermal matrix remodeling via the matrix-metalloproteinase, MMP-13. Therefore, wound-induced cutaneous axon de- and regeneration depend on the coordinated functions of NADPH oxidases mediating distinct processes following injury.

ROS Signaling Mediates Directional Cell Elongation and Somatic Cell Fusion in the Red Alga Griffithsia monilis

In many filamentous red algae, cells that die from physical damage are replaced through somatic fusion of repair cells formed from adjacent cells. We visualized ROS generation in repair cells of Giriffthsia monilis using DCFH-DA staining and examined the expression of the genes involved in wound healing using quantitative PCR. Repair cells elongate along the H₂O₂ gradient, meet at each other’s tips where the H₂O₂ concentration is highest, and undergo somatic fusion. No wound response occurred with ascorbic acid treatment. Conversely, H₂O₂ treatment induced many repair cells, leading to multiple somatic cell fusions. Diphenylene iodonium (DPI) or caffeine treatment reversibly inhibited ROS production in repair cells and blocked the progression of the wound response suggesting that ROS and calcium signaling are involved in the process. Four G. monilis homologues of NADPH-oxidase (GmRBOHs) were identified. The expression of GmRBOHs was upregulated upon injury, peaking 1 h post injury, and decreasing to initial levels when repair cells began to elongate. Our results suggest that ROS generated upon cell injury activates Ca²⁺ channels and upregulates the expression of GmRBOHs, and that H₂O₂ generated from repair cells mediates induced repair cell elongation leading to somatic cell fusion and filament repair.

Endoplasmic Reticulum Stress and Reactive Oxygen Species in Plants

The endoplasmic reticulum (ER) is a key compartment responsible for protein processing and folding, and it also participates in many signal transduction and metabolic processes. Reactive oxygen species (ROS) are important signaling messengers involved in the redox equilibrium and stress response. A number of abiotic and biotic stresses can trigger the accumulation of unfolded or misfolded proteins and lead to ER stress. In recent years, a number of studies have reported that redox metabolism and ROS are closely related to ER stress. ER stress can benefit ROS generation and even cause oxidative burden in plants, finally leading to oxidative stress depending on the degree of ER stress. Moreover, ER stress activates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-mediated ROS signaling, increases antioxidant defense mechanisms, and alters the glutathione (GSH) redox state. Meanwhile, the accumulation of ROS plays a special role in inducing the ER stress response. Given these factors, plants have evolved a series of complex regulatory mechanisms to interact with ROS in response to ER stress. In this review, we summarize the perceptions and responses of plant ER stress and oxidative protein folding in the ER. In addition, we analyze the production and signaling of ROS under ER stress in detail in order to provide a theoretical basis for reducing ER stress to improve the crop survival rate in agricultural applications.

Ferroptosis: A Potential Therapeutic Target in Acute Kidney Injury

Ferroptosis is a recently recognized form of nonapoptotic cell death that is triggered by reactive oxidative species (ROS) due to iron overload, lipid peroxidation accumulation, or the inhibition of phospholipid hydroperoxidase glutathione peroxidase 4 (GPX4). Recent studies have reported that ferroptosis plays a vital role in the pathophysiological process of multiple systems such as the nervous, renal, and pulmonary systems. In particular, the kidney has higher rates of O₂ consumption in its mitochondria than other organs; therefore, it is susceptible to imbalances between ROS and antioxidants. In ischemia/reperfusion (I/R) injury, which is damage caused by the restoring blood flow to ischemic tissues, the release of ROS and reactive nitrogen species is accelerated and contributes to subsequent inflammation and cell death, such as ferroptosis, as well as apoptosis and necrosis being induced. At the same time, I/R injury is one of the major causes of acute kidney injury (AKI), causing significant morbidity and mortality. This review highlights the current knowledge on the involvement of ferroptosis in AKI via oxidative stress.

Pathways Linking Nicotinamide Adenine Dinucleotide Phosphate Production to Endoplasmic Reticulum Protein Oxidation and Stress

The endoplasmic reticulum (ER) lumen is highly oxidizing compared to other subcellular compartments, and maintaining the appropriate levels of oxidizing and reducing equivalents is essential to ER function. Both protein oxidation itself and other essential ER processes, such as the degradation of misfolded proteins and the sequestration of cellular calcium, are tuned to the ER redox state. Simultaneously, nutrients are oxidized in the cytosol and mitochondria to power ATP generation, reductive biosynthesis, and defense against reactive oxygen species. These parallel needs for protein oxidation in the ER and nutrient oxidation in the cytosol and mitochondria raise the possibility that the two processes compete for electron acceptors, even though they occur in separate cellular compartments. A key molecule central to both processes is NADPH, which is produced by reduction of NADP+ during nutrient catabolism and which in turn drives the reduction of components such as glutathione and thioredoxin that influence the redox potential in the ER lumen. For this reason, NADPH might serve as a mediator linking metabolic activity to ER homeostasis and stress, and represent a novel form of mitochondria-to-ER communication. In this review, we discuss oxidative protein folding in the ER, NADPH generation by the major pathways that mediate it, and ER-localized systems that can link the two processes to connect ER function to metabolic activity.

The Regulation of Endoplasmic Reticulum Stress in Cancer: Special Focuses on Luteolin Patents

Cancer is a major health problem across the globe, and is expeditiously growing at a faster rate worldwide. The endoplasmic reticulum (ER) is a membranous cell organelle having inextricable links in cellular homeostasis. Altering ER homeostasis initiates various signaling events known as the unfolded protein response (UPR). The basic purpose of the UPR is to reinstate the homeostasis; however, a continuous UPR can stimulate pathways of cell death, such as apoptosis. As a result, there is great perturbation to target particular signaling pathways of ER stress. Flavonoids have gained significant interest as a potential anticancer agent because of their considerable role in causing cytotoxicity of the cancerous cells. Luteolin, a flavonoid isolated from natural products, is a promising phytochemical used in the treatment of cancer. The current study is designed to review the different endoplasmic reticulum stress pathways involved in the cancer, mechanistic insights of luteolin as an anticancer agent in modulating ER stress, and the available luteolin patent formulations were also highlighted. The patents were selected on the basis of pre-clinical and/or clinical trials, and established antitumor effects using patent databases of FPO IP and Espacenet. The patented formulation of luteolin studied so far has shown promising anticancer potential against different cancer cell lines. However, further research is still required to determine the molecular targets of such bioactive molecules so that they can be used as anticancer drugs.

Basidiomycota Fungi and ROS: Genomic Perspective on Key Enzymes Involved in Generation and Mitigation of Reactive Oxygen Species

Our review includes a genomic survey of a multitude of reactive oxygen species (ROS) related intra- and extracellular enzymes and proteins among fungi of Basidiomycota, following their taxonomic classification within the systematic classes and orders, and focusing on different fungal lifestyles (saprobic, symbiotic, pathogenic). Intra- and extracellular ROS metabolism-involved enzymes (49 different protein families, summing 4170 protein models) were searched as protein encoding genes among 63 genomes selected according to current taxonomy. Extracellular and intracellular ROS metabolism and mechanisms in Basidiomycota are illustrated in detail. In brief, it may be concluded that differences between the set of extracellular enzymes activated by ROS, especially by H2O2, and involved in generation of H2O2, follow the differences in fungal lifestyles. The wood and plant biomass degrading white-rot fungi and the litter-decomposing species of Agaricomycetes contain the highest counts for genes encoding various extracellular peroxidases, mono- and peroxygenases, and oxidases. These findings further confirm the necessity of the multigene families of various extracellular oxidoreductases for efficient and complete degradation of wood lignocelluloses by fungi. High variations in the sizes of the extracellular ROS-involved gene families were found, however, among species with mycorrhizal symbiotic lifestyle. In addition, there are some differences among the sets of intracellular thiol-mediation involving proteins, and existence of enzyme mechanisms for quenching of intracellular H2O2 and ROS. In animal- and plant-pathogenic species, extracellular ROS enzymes are absent or rare. In these fungi, intracellular peroxidases are seemingly in minor role than in the independent saprobic, filamentous species of Basidiomycota. Noteworthy is that our genomic survey and review of the literature point to that there are differences both in generation of extracellular ROS as well as in mechanisms of response to oxidative stress and mitigation of ROS between fungi of Basidiomycota and Ascomycota.

Balancing reactive oxygen species generation by rebooting gut microbiota

Reactive oxygen species (ROS; free radical form O₂ ^•‾ , superoxide radical; OH^• , hydroxyl radical; ROO^• , peroxyl; RO^• , alkoxyl and non-radical form ¹ O₂ , singlet oxygen; H₂ O₂ , hydrogen peroxide) are inevitable companions of aerobic life with crucial role in gut health. But, overwhelming production of ROS can cause serious damage to biomolecules. In this review, we have discussed several sources of ROS production that can be beneficial or dangerous to the human gut. Microorganisms, organelles and enzymes play crucial role in ROS generation, where, NOX1 is the main intestinal enzyme, which produce ROS in the intestine epithelial cells. Previous studies have reported that probiotics play significant role in gut homeostasis by checking the ROS generation, maintaining the antioxidant level, immune system and barrier protection. With current knowledge, we have critically analyzed the available literature and presented the outcome in the form of bubble maps to suggest the probiotics that help in controlling the ROS-specific intestinal diseases, such as inflammatory bowel disease (IBD) and colon cancer. Finally, it has been concluded that rebooting of the gut microbiota with probiotics, postbiotics or fecal microbiota transplantation (FMT) can have crucial implications in the structuring of gut communities for the personalized management of the gastrointestinal (GI) diseases.

Reactive Oxygen Species in Plants: From Source to Sink

Reactive oxygen species (ROS, partial reduction or derivatives of free radicals) are highly reactive, dangerous and can cause oxidative cell death. In addition to their role as toxic by-products of aerobic metabolism, ROS play a role in the control and regulation of biological processes such as growth, the cell cycle, programmed cell death, hormone signaling, biotic and abiotic stress reactions and development. ROS always arise in plants as a by-product of several metabolic processes that are located in different cell compartments, or as a result of the inevitable escape of electrons to oxygen from the electron transport activities of chloroplasts, mitochondria and plasma membranes. These reactive species are formed in chloroplasts, mitochondria, plasma membranes, peroxisomes, apoplasts, the endoplasmic reticulum and cell walls. The action of many non-enzymatic and enzymatic antioxidants present in tissues is required for efficient scavenging of ROS generated during various environmental stressors. The current review provides an in-depth look at the fate of ROS in plants, a beneficial role in managing stress and other irregularities. The production sites are also explained with their negative effects. In addition, the biochemical properties and sources of ROS generation, capture systems, the influence of ROS on cell biochemistry and the crosstalk of ROS with other signaling molecules/pathways are discussed.

Lipotoxicity and β-Cell Failure in Type 2 Diabetes: Oxidative Stress Linked to NADPH Oxidase and ER Stress

A high caloric intake, rich in saturated fats, greatly contributes to the development of obesity, which is the leading risk factor for type 2 diabetes (T2D). A persistent caloric surplus increases plasma levels of fatty acids (FAs), especially saturated ones, which were shown to negatively impact pancreatic β-cell function and survival in a process called lipotoxicity. Lipotoxicity in β-cells activates different stress pathways, culminating in β-cells dysfunction and death. Among all stresses, endoplasmic reticulum (ER) stress and oxidative stress have been shown to be strongly correlated. One main source of oxidative stress in pancreatic β-cells appears to be the reactive oxygen species producer NADPH oxidase (NOX) enzyme, which has a role in the glucose-stimulated insulin secretion and in the β-cell demise during both T1 and T2D. In this review, we focus on the acute and chronic effects of FAs and the lipotoxicity-induced β-cell failure during T2D development, with special emphasis on the oxidative stress induced by NOX, the ER stress, and the crosstalk between NOX and ER stress.

COVID-19: A Redox Disease-What a Stress Pandemic Can Teach Us About Resilience and What We May Learn from the Reactive Species Interactome About Its Treatment

Significance: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus causing coronavirus disease 2019 (COVID-19), affects every aspect of human life by challenging bodily, socioeconomic, and political systems at unprecedented levels. As vaccines become available, their distribution, safety, and efficacy against emerging variants remain uncertain, and specific treatments are lacking. Recent Advances: Initially affecting the lungs, COVID-19 is a complex multisystems disease that disturbs the whole-body redox balance and can be long-lasting (Long-COVID). Numerous risk factors have been identified, but the reasons for variations in susceptibility to infection, disease severity, and outcome are poorly understood. The reactive species interactome (RSI) was recently introduced as a framework to conceptualize how cells and whole organisms sense, integrate, and accommodate stress. Critical Issues: We here consider COVID-19 as a redox disease, offering a holistic perspective of its effects on the human body, considering the vulnerability of complex interconnected systems with multiorgan/multilevel interdependencies. Host/viral glycan interactions underpin SARS-CoV-2's extraordinary efficiency in gaining cellular access, crossing the epithelial/endothelial barrier to spread along the vascular/lymphatic endothelium, and evading antiviral/antioxidant defences. An inflammation-driven "oxidative storm" alters the redox landscape, eliciting epithelial, endothelial, mitochondrial, metabolic, and immune dysfunction, and coagulopathy. Concomitantly reduced nitric oxide availability renders the sulfur-based redox circuitry vulnerable to oxidation, with eventual catastrophic failure in redox communication/regulation. Host nutrient limitations are crucial determinants of resilience at the individual and population level. Future Directions: While inflicting considerable damage to health and well-being, COVID-19 may provide the ultimate testing ground to improve the diagnosis and treatment of redox-related stress diseases. "Redox phenotyping" of patients to characterize whole-body RSI status as the disease progresses may inform new therapeutic approaches to regain redox balance, reduce mortality in COVID-19 and other redox diseases, and provide opportunities to tackle Long-COVID. Antioxid. Redox Signal. 35, 1226-1268.

Nicotinamide Adenine Dinucleotide Phosphate Oxidases in Glucose Homeostasis and Diabetes-Related Endothelial Cell Dysfunction

Oxidative stress within the vascular endothelium, due to excess generation of reactive oxygen species (ROS), is thought to be fundamental to the initiation and progression of the cardiovascular complications of type 2 diabetes mellitus. The term ROS encompasses a variety of chemical species including superoxide anion (O₂^•-), hydroxyl radical (OH^-) and hydrogen peroxide (H₂O₂). While constitutive generation of low concentrations of ROS are indispensable for normal cellular function, excess O₂^•- can result in irreversible tissue damage. Excess ROS generation is catalysed by xanthine oxidase, uncoupled nitric oxide synthases, the mitochondrial electron transport chain and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. Amongst enzymatic sources of O₂^•- the Nox2 isoform of NADPH oxidase is thought to be critical to the oxidative stress found in type 2 diabetes mellitus. In contrast, the transcriptionally regulated Nox4 isoform, which generates H₂O₂, may fulfil a protective role and contribute to normal glucose homeostasis. This review describes the key roles of Nox2 and Nox4, as well as Nox1 and Nox5, in glucose homeostasis, endothelial function and oxidative stress, with a key focus on how they are regulated in health, and dysregulated in type 2 diabetes mellitus.

Early Cytokine-Induced Transient NOX2 Activity Is ER Stress-Dependent and Impacts β-Cell Function and Survival

In type 1 diabetes (T1D) development, proinflammatory cytokines (PIC) released by immune cells lead to increased reactive oxygen species (ROS) production in β-cells. Nonetheless, the temporality of the events triggered and the role of different ROS sources remain unclear. Isolated islets from C57BL/6J wild-type (WT), NOX1 KO and NOX2 KO mice were exposed to a PIC combination. We show that cytokines increase O₂^•− production after 2 h in WT and NOX1 KO but not in NOX2 KO islets. Using transgenic mice constitutively expressing a genetically encoded compartment specific H₂O₂ sensor, we show, for the first time, a transient increase of cytosolic/nuclear H₂O₂ in islet cells between 4 and 5 h during cytokine exposure. The H₂O₂ increase coincides with the intracellular NAD(P)H decrease and is absent in NOX2 KO islets. NOX2 KO confers better glucose tolerance and protects against cytokine-induced islet secretory dysfunction and death. However, NOX2 absence does not counteract the cytokine effects in ER Ca²⁺ depletion, Store-Operated Calcium Entry (SOCE) increase and ER stress. Instead, the activation of ER stress precedes H₂O₂ production. As early NOX2-driven ROS production impacts β-cells’ function and survival during insulitis, NOX2 might be a potential target for designing therapies against early β-cell dysfunction in the context of T1D onset.

Effects of different intensities of continuous training on vascular inflammation and oxidative stress in spontaneously hypertensive rats

We aimed to study the effects and underlying mechanism of different intensities of continuous training (CT) on vascular inflammation and oxidative stress in spontaneously hypertensive rats (SHR). Rats were divided into five groups (n = 12): Wistar‐Kyoto rats sedentary group (WKY‐S), sedentary group (SHR‐S), low‐intensity CT group (SHR‐L), medium‐intensity CT group (SHR‐M) and high‐intensity CT group (SHR‐H). Changes in body mass, heart rate and blood pressure were recorded. The rats were euthanized after 14 weeks, and blood and vascular tissue samples were collected. Haematoxylin and Eosin staining was used to observe the aortic morphology, and Western blot was used to detect the expression of mesenteric artery proteins. After CT, the mean arterial pressures improved in SHR‐L and SHR‐M and increased in SHR‐H compared with those in SHR‐S. Vascular inflammation and oxidative stress levels significantly subsided in SHR‐L and SHR‐M (p < 0.05), whereas in SHR‐H, only vascular inflammation significantly subsided (p < 0.05), and oxidative stress remained unchanged (p > 0.05). AMPK and SIRT1/3 expressions in SHR‐L and SHR‐M were significantly up‐regulated than those in SHR‐S (p < 0.05). These results indicated that low‐ and medium‐intensity CT can effectively reduce the inflammatory response and oxidative stress of SHR vascular tissue, and high‐intensity CT can improve vascular tissue inflammation but not oxidative stress.

Pelargonic acid vanillylamide and rosuvastatin protect against oxidized low-density lipoprotein-induced endothelial dysfunction by inhibiting the NF-κB/NLRP3 pathway and improving cell-cell junctions

Oxidized low-density lipoprotein (ox-LDL) not only causes hyperlipidemia and contributes to atherosclerosis but also induces the endothelial dysfunction that leads to cardiovascular diseases. The nuclear factor-kappa B (NF-κB) pathway plays a key role in many chronic disorders and is a transcriptional factor in various inflammatory responses. The present study aimed to investigate the synergistic effects of pelargonic acid vanillylamide (PAVA) and rosuvastatin (RSV) on ox-LDL-induced inflammatory responses in human vascular endothelial cells (HUV-EC-C). HUV-EC-C were pretreated with PAVA or RSV and their combination for 2 h followed by ox-LDL for 24 h. The MTT assay was used to measure mitochondrial function. The DCFH-DA assay was used to evaluate oxidative phosphorylation, and western blotting was used to measured NF-κB/NLRP3 and related signaling pathways in HUV-EC-C. Ox-LDL induced lectin-type oxidized LDL receptor 1 (LOX-1) expression, NADPH oxidase 4 activation, and the overexpression of reactive oxygen species, which were inhibited by pretreatment with the combination of PAVA and RSV. Moreover, PAVA and RSV inhibited ox-LDL-induced NF-κBp65 activation. Ox-LDL induced NF-κB/NLRP3 pathway activation by inducing C-reactive protein expression, NLRP3 activation, caspase-1 activation, and IL-1β secretion, which were inhibited by pretreatment with the combination of PAVA and RSV. The combination of PAVA and RSV reduced ox-LDL-induced recruitment of monocytes to the site of inflammation, inhibited activation of the NLRP3 inflammasome, and ameliorated the impairment of cell-cell junctions through the NF-κB pathway. Our results suggest that the synergistic effects of PAVA and RSV provide a novel mechanism for the treatment of cardiovascular diseases.

Oxidative Stress and Hypertension

A link between oxidative stress and hypertension has been firmly established in multiple animal models of hypertension but remains elusive in humans. While initial studies focused on inactivation of nitric oxide by superoxide, our understanding of relevant reactive oxygen species (superoxide, hydrogen peroxide, and peroxynitrite) and how they modify complex signaling pathways to promote hypertension has expanded significantly. In this review, we summarize recent advances in delineating the primary and secondary sources of reactive oxygen species (nicotinamide adenine dinucleotide phosphate oxidases, uncoupled endothelial nitric oxide synthase, endoplasmic reticulum, and mitochondria), the posttranslational oxidative modifications they induce on protein targets important for redox signaling, their interplay with endogenous antioxidant systems, and the role of inflammasome activation and endoplasmic reticular stress in the development of hypertension. We highlight how oxidative stress in different organ systems contributes to hypertension, describe new animal models that have clarified the importance of specific proteins, and discuss clinical studies that shed light on how these processes and pathways are altered in human hypertension. Finally, we focus on the promise of redox proteomics and systems biology to help us fully understand the relationship between ROS and hypertension and their potential for designing and evaluating novel antihypertensive therapies.

Molecular nature and physiological role of the mitochondrial calcium uniporter channel

Calcium (Ca2+) signaling is critical for cell function and cell survival. Mitochondria play a major role in regulating the intracellular Ca2+ concentration ([Ca2+]i). Mitochondrial Ca2+ uptake is an important determinant of cell fate and governs respiration, mitophagy/autophagy, and the mitochondrial pathway of apoptosis. Mitochondrial Ca2+ uptake occurs via the mitochondrial Ca2+ uniporter (MCU) complex. This review summarizes the present knowledge on the function of MCU complex, regulation of MCU channel, and the role of MCU in Ca2+ homeostasis and human disease pathogenesis. The channel core consists of four MCU subunits and essential MCU regulators (EMRE). Regulatory proteins that interact with them include mitochondrial Ca2+ uptake 1/2 (MICU1/2), MCU dominant-negative β-subunit (MCUb), MCU regulator 1 (MCUR1), and solute carrier 25A23 (SLC25A23). In addition to these proteins, cardiolipin, a mitochondrial membrane-specific phospholipid, has been shown to interact with the channel core. The dynamic interplay between the core and regulatory proteins modulates MCU channel activity after sensing local changes in [Ca2+]i, reactive oxygen species, and other environmental factors. Here, we highlight the structural details of the human MCU heteromeric assemblies and their known roles in regulating mitochondrial Ca2+ homeostasis. MCU dysfunction has been shown to alter mitochondrial Ca2+ dynamics, in turn eliciting cell apoptosis. Changes in mitochondrial Ca2+ uptake have been implicated in pathological conditions affecting multiple organs, including the heart, skeletal muscle, and brain. However, our structural and functional knowledge of this vital protein complex remains incomplete, and understanding the precise role for MCU-mediated mitochondrial Ca2+ signaling in disease requires further research efforts.

Endothelial Nox4 dysfunction aggravates atherosclerosis by inducing endoplasmic reticulum stress and soluble epoxide hydrolase

BACKGROUND AND AIMS

Our previous findings have demonstrated the protective effect of endothelial Nox4-based NADPH oxidase on atherosclerosis. One of the possible mechanisms is the inhibition of soluble epoxide hydrolase (sEH), a proinflammatory and atherogenic factor. Our goal was to investigate whether in vivo inhibition of sEH by 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU) alleviates endothelial Nox4 dysfunction caused atherosclerosis and the regulatory mechanism of endothelial Nox4 on sEH.

METHODS

& results: We used endothelial human Nox4 dominant-negative (EDN) transgenic mice in ApoE deficient background to mimic the dysfunction of endothelial Nox4 in atherosclerosis-prone conditions. In EDN aortic endothelium, sEH and the inflammatory marker vascular cell adhesion molecule 1 (VCAM1) were upregulated. TPPU reduced atherosclerotic lesions in EDN mice. In EDN endothelial cells (ECs), the endoplasmic reticulum (ER) stress markers (BIP, IRE1α, phosphorylation of PERK, ATF6) were upregulated, and they can be suppressed by ER stress inhibitor 4-phenyl butyric acid (4-PBA). In EDN ECs, 4-PBA downregulated the expression of sEH and VCAM1, suppressed inflammation, and its application in vivo reduced atherosclerotic lesions of EDN mice.

CONCLUSIONS

Endothelial Nox4 dysfunction upregulated sEH to enhance inflammation, probably by its induction of ER stress. Inhibition of ER stress or sEH is beneficial to alleviate atherosclerosis caused by endothelial Nox4 dysfunction.

Functions of ROS in Macrophages and Antimicrobial Immunity

Reactive oxygen species (ROS) are a chemically defined group of reactive molecules derived from molecular oxygen. ROS are involved in a plethora of processes in cells in all domains of life, ranging from bacteria, plants and animals, including humans. The importance of ROS for macrophage-mediated immunity is unquestioned. Their functions comprise direct antimicrobial activity against bacteria and parasites as well as redox-regulation of immune signaling and induction of inflammasome activation. However, only a few studies have performed in-depth ROS analyses and even fewer have identified the precise redox-regulated target molecules. In this review, we will give a brief introduction to ROS and their sources in macrophages, summarize the versatile roles of ROS in direct and indirect antimicrobial immune defense, and provide an overview of commonly used ROS probes, scavengers and inhibitors.

NADPH Oxidase 5 Induces Changes in the Unfolded Protein Response in Human Aortic Endothelial Cells and in Endothelial-Specific Knock-in Mice

Oxidative stress constitutes a key molecular mechanism in the development of cardiovascular diseases. A potential relationship between reactive oxygen species (ROS) driven by the NADPH oxidase family (NOX) and the unfolded protein response (UPR) has been postulated. Nevertheless, there is a lack of information about the crosstalk between NOX5 homologue and the UPR in a cardiovascular context. The main aim was to analyze NOX5-mediated ROS effects in the UPR and its importance in cardiovascular diseases. To this effect, we used an adenoviral NOX5-β overexpression model in human aortic endothelial cells (HAEC) and a conditional endothelial NOX5 knock-in mouse. Using expression arrays, we investigated NOX5-induced genomic changes in HAEC. Compared with the control HAEC, 298 genes were differentially expressed. Gene ontology analysis revealed the activation of numerous cellular routes, the most relevant being the UPR pathway. Using real-time PCR and Western Blot experiments, we confirmed that NOX5 overexpression induced changes in the expression of the UPR components, which were associated with increased apoptosis. Moreover, in endothelial-specific NOX5 knock-in mice, we found changes in the expression of the UPR components genes. In these mice, myocardial infarction was performed by permanent coronary artery ligation; however, NOX5 expression was not associated with differences in the UPR components mRNA levels. In these animals, we found significant associations between the UPR components gene expression and echocardiographic parameters. Our data support the idea that NOX5-derived ROS may modulate the UPR pathway in endothelial cells, which might play a relevant role in cardiac physiology.

STING, the Endoplasmic Reticulum, and Mitochondria: Is Three a Crowd or a Conversation?

The anti-viral pattern recognition receptor STING and its partnering cytosolic DNA sensor cGAS have been increasingly recognized to respond to self DNA in multiple pathologic settings including cancer and autoimmune disease. Endogenous DNA sources that trigger STING include damaged nuclear DNA in micronuclei and mitochondrial DNA (mtDNA). STING resides in the endoplasmic reticulum (ER), and particularly in the ER-mitochondria associated membranes. This unique location renders STING well poised to respond to intracellular organelle stress. Whereas the pathways linking mtDNA and STING have been addressed recently, the mechanisms governing ER stress and STING interaction remain more opaque. The ER and mitochondria share a close anatomic and functional relationship, with mutual production of, and inter-organelle communication via calcium and reactive oxygen species (ROS). This interdependent relationship has potential to both generate the essential ligands for STING activation and to regulate its activity. Herein, we review the interactions between STING and mitochondria, STING and ER, ER and mitochondria (vis-à-vis calcium and ROS), and the evidence for 3-way communication.

Post-Translational Modification of Cysteines: A Key Determinant of Endoplasmic Reticulum-Mitochondria Contacts (MERCs)

Cells must adjust their redox state to an ever-changing environment that could otherwise result in compromised homeostasis. An obvious way to adapt to changing redox conditions depends on cysteine post-translational modifications (PTMs) to adapt conformation, localization, interactions and catalytic activation of proteins. Such PTMs should occur preferentially in the proximity of oxidative stress sources. A particular concentration of these sources is found near membranes where the endoplasmic reticulum (ER) and the mitochondria interact on domains called MERCs (Mitochondria-Endoplasmic Reticulum Contacts). Here, fine inter-organelle communication controls metabolic homeostasis. MERCs achieve this goal through fluxes of Ca²⁺ ions and inter-organellar lipid exchange. Reactive oxygen species (ROS) that cause PTMs of mitochondria-associated membrane (MAM) proteins determine these intertwined MERC functions. Chronic changes of the pattern of these PTMs not only control physiological processes such as the circadian clock but could also lead to or worsen many human disorders such as cancer and neurodegenerative diseases.

Mini review: immunologic functions of dual oxidases in mucosal systems of vertebrates

Abstract Mucosal epithelial cells act as the first immunologic barrier of organisms, and contact directly with pathogens. Therefore, hosts must have differential strategies to combat pathogens efficiently. Reactive oxygen species (ROS), as a kind of oxidizing agents, participates in the early stage of killing pathogens quickly. Recent reports have revealed that dual oxidase (DUOX) plays a key role in mucosal immunity. And the DUOX is a transmembrane protein which produces ROS as their primary enzymatic products. This process is an important pattern for eliminating pathogens. In this review, we highlight the DUOX immunologic functions in the respiratory and digestive tract of vertebrates.

Pathways for Sensing and Responding to Hydrogen Peroxide at the Endoplasmic Reticulum

The endoplasmic reticulum (ER) has emerged as a source of hydrogen peroxide (H₂O₂) and a hub for peroxide-based signaling events. Here we outline cellular sources of ER-localized peroxide, including sources within and near the ER. Focusing on three ER-localized proteins-the molecular chaperone BiP, the transmembrane stress-sensor IRE1, and the calcium pump SERCA2-we discuss how post-translational modification of protein cysteines by H₂O₂ can alter ER activities. We review how changed activities for these three proteins upon oxidation can modulate signaling events, and also how cysteine oxidation can serve to limit the cellular damage that is most often associated with elevated peroxide levels.

Regulation of Vascular Calcification by Reactive Oxygen Species

Vascular calcification is the deposition of hydroxyapatite crystals in the medial or intimal layers of arteries that is usually associated with other pathological conditions including but not limited to chronic kidney disease, atherosclerosis and diabetes. Calcification is an active, cell-regulated process involving the phenotype transition of vascular smooth muscle cells (VSMCs) from contractile to osteoblast/chondrocyte-like cells. Diverse triggers and signal transduction pathways have been identified behind vascular calcification. In this review, we focus on the role of reactive oxygen species (ROS) in the osteochondrogenic phenotype switch of VSMCs and subsequent calcification. Vascular calcification is associated with elevated ROS production. Excessive ROS contribute to the activation of certain osteochondrogenic signal transduction pathways, thereby accelerating osteochondrogenic transdifferentiation of VSMCs. Inhibition of ROS production and ROS scavengers and activation of endogenous protective mechanisms are promising therapeutic approaches in the prevention of osteochondrogenic transdifferentiation of VSMCs and subsequent vascular calcification. The present review discusses the formation and actions of excess ROS in different experimental models of calcification, and the potential of ROS-lowering strategies in the prevention of this deleterious condition.

Research status and prgoress of nonalcoholic fatty pancreatic disease

Nonalcoholic fatty pancreatic disease (NAFPD) is a disease characterized by an increase in pancreatic fat accumulation. It is a component of the metabolic syndrome and often coexists with nonalcoholic fatty liver disease. Once the diagnosis is established, it is closely related to acute and chronic pancreatitis, type 2 diabetes mellitus, pancreatic fibrosis, and pancreatic cancer. In recent years, it has been confirmed that NAFPD is closely related to cardiovascular disease, liver fibrosis, and liver cancer. The prevalence of NAFPD ranges between 11% and 69%, and increases with age. It is worth noting that the prevalence in obese children is twice as high as that in non-obese children. The high prevalence rate and complexity of the disease have aroused people's high attention. Therefore, to improve the understanding of NAFPD, fully understand the clinical significance of NAFPD, and further study its pathogenesis, diagnosis, and treatment require the collaboration and joint efforts of multiple disciplines, including hepatopathy, gastroenterology, endocrine metabolism, cardiovascular disease, imaging, pathology, and others. In this paper, we review the clinical significance, pathogenesis, and imaging diagnosis of NAFPD and propose our personal understanding of the key points in future research.

The correlation of IRE1α oxidation with Nox4 activation in aging-associated vascular dysfunction

Oxidative stress attributable to the activation of a Nox4-containing NADPH oxidase is involved in aging-associated vascular dysfunction. However, the Nox4-induced signaling mechanism for the vascular alteration in aging remains unclear. In an aged aorta, the expression of Nox4 mRNA and protein by Nox family of genes was markedly increased compared with a young aorta. Nox4 localization mainly to ER was also established. In the aorta of Nox4 WT mice aged 23–24 months (aged), reactive oxygen species (ROS) and endoplasmic reticulum (ER)/oxidative stress were markedly increased compared with the counter KO mice. Furthermore, endothelial functions including eNOS coupling process and acetylcholine-induced vasodilation were significantly disturbed in the aged WT, slightly affected in the counter KO aorta. Consistently, in d-galactose-induced in vitro aging condition, ER-ROS and its associated ER Nox4 expression and activity were highly increased. Also, in chronic d-galactose-treated condition, IRE1α phosphorylation and XBP-1 splicing and were transiently increased, but IRE1α sulfonation was robustly increased in the aging Nox4 WT condition when compared to the counter KO condition. In vitro D-gal-induced aging study, the phenomenon were abrogated with Nox4 knock-down condition and was significantly decreased in GKT, Nox4 inhibitor and 4-PBA, ER chemical chaperone-treated human umbilical vein endothelial cells. The state of Nox4-based ER redox imbalance/ROS accumulation is suggested to determine the pathway “the UPR; IRE1α phosphorylation and XBP-1 splicing and the UPR failure; IRE1α cysteine-based oxidation, especially sulfonation, finally controlling aging-associated vascular dysfunction.

Beneficial Effect of Chloroquine and Amodiaquine on Type 1 Diabetic Tubulopathy by Attenuating Mitochondrial Nox4 and Endoplasmic Reticulum Stress

BACKGROUND

Oxidative stress induced by chronic hyperglycemia is recognized as a significant mechanistic contributor to the development of diabetic kidney disease (DKD). Nonphagocytic nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) is a major source of reactive oxygen species (ROS) in many cell types and in the kidney tissue of diabetic animals. We designed this study to explore the therapeutic potential of chloroquine (CQ) and amodiaquine (AQ) for inhibiting mitochondrial Nox4 and diabetic tubular injury.

METHODS

Human renal proximal tubular epithelial cells (hRPTCs) were cultured in high-glucose media (30 mM D-glucose), and diabetes was induced with streptozotocin (STZ, 50 mg/kg i.p. for 5 days) in male C57BL/6J mice. CQ and AQ were administered to the mice via intraperitoneal injection for 14 weeks.

RESULTS

CQ and AQ inhibited mitochondrial Nox4 and increased mitochondrial mass in hRPTCs under high-glucose conditions. Reduced mitochondrial ROS production after treatment with the drugs resulted in decreased endoplasmic reticulum (ER) stress, suppressed inflammatory protein expression and reduced cell apoptosis in hRPTCs under high-glucose conditions. Notably, CQ and AQ treatment diminished Nox4 activation and ER stress in the kidneys of STZ-induced diabetic mice. In addition, we observed attenuated inflammatory protein expression and albuminuria in STZ-induced diabetic mice after CQ and AQ treatment.

CONCLUSION

We substantiated the protective actions of CQ and AQ in diabetic tubulopathy associated with reduced mitochondrial Nox4 activation and ER stress alleviation. Further studies exploring the roles of mitochondrial Nox4 in the pathogenesis of DKD could suggest new therapeutic targets for patients with DKD.

Interrelation between ROS and Ca2+ in aging and age-related diseases

Calcium (Ca2+) and reactive oxygen species (ROS) are versatile signaling molecules coordinating physiological and pathophysiological processes. While channels and pumps shuttle Ca2+ ions between extracellular space, cytosol and cellular compartments, short-lived and highly reactive ROS are constantly generated by various production sites within the cell. Ca2+ controls membrane potential, modulates mitochondrial adenosine triphosphate (ATP) production and affects proteins like calcineurin (CaN) or calmodulin (CaM), which, in turn, have a wide area of action. Overwhelming Ca2+ levels within mitochondria efficiently induce and trigger cell death. In contrast, ROS comprise a diverse group of relatively unstable molecules with an odd number of electrons that abstract electrons from other molecules to gain stability. Depending on the type and produced amount, ROS act either as signaling molecules by affecting target proteins or as harmful oxidative stressors by damaging cellular components. Due to their wide range of actions, it is little wonder that Ca2+ and ROS signaling pathways overlap and impact one another. Growing evidence suggests a crucial implication of this mutual interplay on the development and enhancement of age-related disorders, including cardiovascular and neurodegenerative diseases as well as cancer.

AGE/RAGE signaling-mediated endoplasmic reticulum stress and future prospects in non-coding RNA therapeutics for diabetic nephropathy

Disturbance of endoplasmic reticulum (ER) homeostasis triggered by the accumulation of unfolded proteins and advanced glycation end-products (AGEs) plays a major role in pathophysiology of diabetic nephropathy. Activation of receptor for AGEs (RAGE) stimulates NADPH oxidase-mediated reactive oxygen species (ROS) production, leading to ER stress, inflammation, glomerular hypertrophy, podocyte injury, and renal fibrosis. A growing body of evidence indicates that non-coding RNAs (ncRNAs) could rescue ER stress and renal inflammation by the epigenetic modification. This review summarizes ncRNA regulation in AGE/RAGE signaling-mediated ER stress, and discusses the opportunities and challenges of ncRNA-loaded extracellular vesicle therapy in diabetic nephropathy.

The roles of ER stress in epilepsy: Molecular mechanisms and therapeutic implications

Epilepsies are a diverse group of neurological disorders, which are characterized by spontaneous recurrent seizures. Although a wide range of pathogenic mechanisms such as alterations in ion channels, inflammation and neuronal loss have been reported to be implicated in the epileptogenesis, the underlying pathogenesis of epilepsy remains unclear currently. Endoplasmic reticulum (ER) stress is regarded as a condition that unfolded or misfolded proteins accumulate in the ER lumen. Excessive or prolonged ER stress causes the activation of the unfolded protein response (UPR) to buffer ER stress and restore ER homeostasis. Increasing evidence has indicated dysregulated ER stress during epileptogenesis, which may participate in various pathological processes associated with epilepsy. In this present review, we summarized recent advances in the involvement of ER stress in the pathogenesis of epilepsy. Additionally, the antiepileptic and neuroprotective effects of interventions targeting ER stress were also discussed.

Role of nitric oxide in the response to photooxidative stress in prostate cancer cells

A continuous state of oxidative stress during inflammation contributes to the development of 25% of human cancers. Epithelial and inflammatory cells release reactive oxygen species (ROS) and reactive nitrogen species (RNS) that can damage DNA. ROS/RNS have biological implications in both chemoresistance and tumor recurrence. As several clinically employed anticancer drugs can generate ROS/RNS, we have addressed herein how inducible nitric oxide synthase and nitric oxide (iNOS/^•NO) affect the molecular pathways implicated in the tumor response to oxidative stress. To mimic the oxidative stress associated with chemotherapy, we used a photosensitizer (pheophorbide a) that can generate ROS/RNS in a controlled manner. We investigated how iNOS/^•NO modulates the tumor response to oxidative stress by involving the NF-κB and Nrf2 molecular pathways. We found that low levels of iNOS induce the development of a more aggressive tumor population, leading to survival, recurrence and resistance. By contrast, high levels of iNOS/^•NO sensitize tumor cells to oxidative treatment, causing cell growth arrest. Our analysis showed that NF-κB and Nrf2, which are activated in response to oxidative stress, communicate with each other through RKIP. For this critical role, RKIP could be an interesting target for anticancer drugs. Our study provides insight into the complex signaling response of cancer cells to oxidative treatments as well as new possibilities for the rational design of new therapeutic strategies.

Peri/Epicellular Thiol Oxidoreductases as Mediators of Extracellular Redox Signaling

Significance: Supracellular redox networks regulating cell-extracellular matrix (ECM) and organ system architecture merge with structural and functional (catalytic or allosteric) properties of disulfide bonds. This review addresses emerging evidence that exported thiol oxidoreductases (TORs), such as thioredoxin, protein disulfide isomerases (PDIs), quiescin sulfhydryl oxidases (QSOX)1, and peroxiredoxins, composing a peri/epicellular (pec)TOR pool, mediate relevant signaling. pecTOR functions depend mainly on kinetic and spatial regulation of thiol-disulfide exchange reactions governed by redox potentials, which are modulated by exported intracellular low-molecular-weight thiols, together conferring signal specificity. Recent Advances: pecTOR redox-modulates several targets including integrins, ECM proteins, surface molecules, and plasma components, although clear-cut documentation of direct effects is lacking in many cases. TOR catalytic pathways, displaying common patterns, culminate in substrate thiol reduction, oxidation, or isomerization. Peroxiredoxins act as redox/peroxide sensors, contrary to PDIs, which are likely substrate-targeted redox modulators. Emerging evidence suggests important pecTOR roles in patho(physio)logical processes, including blood coagulation, vascular remodeling, mechanosensing, endothelial function, immune responses, and inflammation. Critical Issues: Effects of pecPDIs supporting thrombosis/platelet activation have been well documented and reached the clinical arena. Roles of pecPDIA1 in vascular remodeling/mechanosensing are also emerging. Extracellular thioredoxin and pecPDIs redox-regulate immunoinflammation. Routes of TOR externalization remain elusive and appear to involve Golgi-independent routes. pecTORs are particularly accessible drug targets. Future Directions: Further understanding mechanisms of thiol redox reactions and developing assays for assessing pecTOR redox activities remain important research avenues. Also, addressing pecTORs as disease markers and achieving more efficient/specific drugs for pecTOR modulation are major perspectives for diagnostic/therapeutic improvements.

Long-term 1-nitropyrene exposure induces endoplasmic reticulum stress and inhibits steroidogenesis in mice testes

1-Nitropyrene (1-NP) is a representative nitro-polycyclic aromatic hydrocarbon from diesel exhaust. Recently, we found that maternal 1-NP exposure caused fetal growth retardation and disturbed cognitive development in adolescent female offspring. To investigate long-term 1-NP exposure on spermatogenesis and steroidogenesis, male mice were exposed to 1-NP (1.0 mg/kg/day) by gavage for 70 days. There was no significant difference on relative testicular weight, number of testicular apoptotic cells and epididymal sperm count between 1-NP-exposed mice and controls. Although long-term 1-NP exposure did not influence number of Leydig cells, steroidogenic genes and enzymes, including STAR, P450scc, P45017α and 17β-HD, were downregulated in 1-NP-expoed mouse testes. Correspondingly, serum and testicular testosterone (T) levels were reduced in 1-NP-exposed mice. Additional experiment showed that testicular GRP78 mRNA and protein were upregulated by 1-NP. Testicular phospho-IRE1α and sliced xbp-1 mRNA, a downstream molecule of IRE1α, were elevated in 1-NP-exposed mice. Testicular phospho-PERK and phospho-eIF2α, a downstream molecule of PERK pathway, were increased in 1-NP-exposed mice. Testicular NOX4, a subunit of NAPDH oxidase, and HO-1, MDA, two oxidative stress markers, were increased in 1-NP-exposed mice. Testicular GSH and GSH/GSSG were decreased in 1-NP-exposed mice. These results suggest that long-term 1-NP exposure induces reactive oxygen species-evoked ER stress and disrupts steroidogenesis in mouse testes.

Pyridine nucleotide regulation of hepatic endoplasmic reticulum calcium uptake

Pyridine nucleotides serve an array of intracellular metabolic functions such as, to name a few, shuttling electrons in enzymatic reactions, safeguarding the redox state against reactive oxygen species, cytochrome P450 (CYP) enzyme detoxification pathways and, relevant to this study, the regulation of ion fluxes. In particular, the maintenance of a steep calcium gradient between the cytosol and endoplasmic reticulum (ER), without which apoptosis ensues, is achieved by an elaborate combination of energy–requiring ER membrane pumps and efflux channels. In liver microsomes, net calcium uptake was inhibited by physiological concentrations of NADP. In the presence of 1 mmol/L NADP, calcium uptake was attenuated by nearly 80%, additionally, this inhibitory effect was blunted by concomitant addition of NADPH. No other nicotinamide containing compounds ‐save a slight inhibition by NAADP‐hindered calcium uptake; thus, only oxidized pyridine nucleotides, or related compounds with a phosphate moiety, had an imposing effect. Moreover, the NADP inhibition was evident even after selectively blocking ER calcium efflux channels. Given the fundamental role of endoplasmic calcium homeostasis, it is plausible that changes in cytosolic NADP concentration, for example, during anabolic processes, could regulate net ER calcium uptake.