Multifaceted roles of NADPH oxidases in the growth and pathogenicity of Beauveria bassiana

Reactive oxygen species (ROS), synthesized by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) complex, are vital molecules in biological cells, influencing various physiological processes such as fungal growth, development, and virulence. Beauveria bassiana, an entomopathogenic fungus, is a promising biopesticide for agricultural, forestry, and urban pest control. This study focuses on the characterization of NADPH oxidases (Noxs) in B. bassiana. Gene expression profiles of Noxs in B. bassiana (BbNoxs) were analysed using RT-qPCR. Knockout strains of single BbNoxA, BbNoxB, BbNoxR, and double BbNoxA and BbNoxB were constructed via homologous recombination, and their phenotypic characteristics were examined. Fungal virulence was evaluated using Galleria mellonella larvae, and infection structures formation and penetration ability were assessed on cicada wings. ROS production and actin assembly during fungal growth and infection were detected using staining and marker methods. Expression analysis revealed significant upregulation of BbNoxs during fungal growth and infection. Compared to the wild-type strain, single knockouts (ΔBbNoxA/B/R) and double knockout (ΔBbNoxAB) of BbNoxs exhibited reduced conidial yields, accelerated conidial germination rates. Deletion of BbNoxB or BbNoxR decreased fungal virulence compared to the WT strain in topical inoculation experiments. Additionally, loss of BbNoxB or BbNoxR impaired infection structures formation, penetration ability, ROS production, and actin aggregation during fungal infection. BbNoxs are crucial for fungal growth, development, and virulence in B. bassiana, playing essential roles in infection structures formation, penetration, ROS production, and actin assembly. Understanding their functions provides insights into B. bassiana's pathogenic mechanisms.

NADPH oxidase 1/4 dual inhibitor setanaxib suppresses platelet activation and thrombus formation

AIMS

The production of reactive oxygen species (ROS) by NADPH oxidase (NOX) is able to induce platelet activation, making NOX a promising target for antiplatelet therapy. In this study, we examined the effects of setanaxib, a dual NOX1/4 inhibitor, on human platelet function and ROS-related signaling pathways.

MATERIALS AND METHODS

In collagen-stimulated human platelets, aggregometry, assessment of ROS and Ca2+, immunoblotting, ELISA, flow cytometry, platelet adhesion assay, and assessment of mouse arterial thrombosis were performed in this study.

KEY FINDINGS

Setanaxib inhibited both intracellular and extracellular ROS production in collagen-activated platelets. Additionally, setanaxib significantly inhibited collagen-induced platelet aggregation, P-selectin exposure from α-granule release, and ATP release from dense granules. Setanaxib blocked the specific tyrosine phosphorylation-mediated activation of Syk, LAT, Vav1, and Btk within collagen receptor signaling pathways, leading to reduced activation of PLCγ2, PKC, and Ca2+ mobilization. Setanaxib also inhibited collagen-induced activation of integrin αIIbβ3, which is linked to increased cGMP levels and VASP phosphorylation. Furthermore, setanaxib suppressed collagen-induced p38 MAPK activation, resulting in decreased phosphorylation of cytosolic PLA2 and reduced TXA2 generation. Setanaxib also inhibited ERK5 activation, affecting the exposure of procoagulant phosphatidylserine. Setanaxib reduced thrombus formation under shear conditions by preventing platelet adhesion to collagen. Finally, in vivo administration of setanaxib in animal models led to the inhibition of arterial thrombosis.

SIGNIFICANCE

This study is the first to show that setanaxib suppresses ROS generation, platelet activation, and collagen-induced thrombus formation, suggesting its potential use in treating thrombotic or cardiovascular diseases.

Intact NOX2 in T Cells Mediates Pregnancy-Induced Renal Damage in Dahl SS Rats

BACKGROUND

Hypertensive disorders of pregnancy are associated with increased risk for cardiovascular disease, renal disease, and mortality. While the exact mechanisms remain unclear, T cells and reactive oxygen species have been implicated in its pathogenesis. We utilized Dahl salt-sensitive (SS), SSCD247-/- (Dahl SS CD247 knockout rat; lacking T cells), and SSp67phox-/- (Dahl SS p67phox [NOX2 (NADPH [nitcotinamide adenine dinucleotide phosphate] oxidase 2)] knockout rat; lacking NOX2) rats to investigate these mechanisms in primigravida and multigravida states.

METHODS

We assessed blood pressure and renal damage phenotypes in SS, SSCD247-/-, and SSp67phox-/- rats during primigravida and multigravida states. To investigate the contribution of NOX2 in T cells, we performed adoptive transfers of splenocytes or cluster of differentiation (CD)4+ T cells from either SS or SSp67phox-/- donors into SSCD247-/- recipients to determine pregnancy-specific alterations in phenotype.

RESULTS

Multigravida SS rats developed significant pregnancy-induced renal damage and renal functional impairment associated with elevated maternal mortality rates, whereas deletion of T cells or NOX2 garnered protection. During primigravida states, this attenuation in renal damage was observed, with the greatest protection in the SSp67phox-/- rat. To demonstrate that NOX2 in T cells contributes to adverse pregnancy phenotypes, adoptive transfer of SS splenocytes into SSCD247-/- rats resulted in significant pregnancy-induced renal damage, whereas transfer of SSp67phox-/- splenocytes garnered protection. Specifically, the transfer of SS CD4+ T cells resulted in pregnancy-induced proteinuria and increases in uterine artery resistance index, an effect not seen with the transfer of SSp67phox-/- CD4+ T cells.

CONCLUSIONS

T cells and NOX2-derived reactive oxygen species, thus, contribute to end-organ damage in both primigravida and multigravida pregnancies in the SS rat leading to increases in maternal mortality.

Self-extinguishing relay waves enable homeostatic control of human neutrophil swarming

Neutrophils collectively migrate to sites of injury and infection. How these swarms are coordinated to ensure the proper level of recruitment is unknown. Using an ex vivo model of infection, we show that human neutrophil swarming is organized by multiple pulsatile chemoattractant waves. These waves propagate through active relay in which stimulated neutrophils trigger their neighbors to release additional swarming cues. Unlike canonical active relays, we find these waves to be self-terminating, limiting the spatial range of cell recruitment. We identify an NADPH-oxidase-based negative feedback loop that is needed for this self-terminating behavior. We observe near-constant levels of neutrophil recruitment over a wide range of starting conditions, revealing surprising robustness in the swarming process. This homeostatic control is achieved by larger and more numerous swarming waves at lower cell densities. We link defective wave termination to a broken recruitment homeostat in the context of human chronic granulomatous disease.

Advanced glycation end products promote ROS production via PKC/p47 phox axis in skeletal muscle cells

Advanced glycation end products (AGEs) are risk factors for various diseases, including sarcopenia. One of the deleterious effects of AGEs is the induction of abnormal reactive oxygen species (ROS) production in skeletal muscle. However, the underlying mechanism remains poorly understood. Therefore, the aim of this study was to elucidate how AGEs induce ROS production in skeletal muscle cells. This study demonstrated that AGEs treatment promoted ROS production in myoblasts and myotubes while PKC inhibitor abolished ROS production by AGEs stimulation. Phosphorylation of p47 phox by kinases such as PKCα is required to form the Nox2 complex, which induces ROS production. In this study, AGEs treatment promoted the phosphorylation of PKCα and p47 phox in myoblasts and myotubes. Our findings suggest that AGEs promote ROS production through the phosphorylation of PKCα and p47 phox in skeletal muscle cells.

Development of New Peptidomimetic NADPH Oxidase Inhibitors with Antithrombotic Properties

The ability of synthetic peptides inhibitors of NOX1 to effectively block the production of ROS by the enzyme was studied with different methodologies. Specifically, taking advantage of our understanding of the active epitope of the regulatory NOX1 subunit NOXA1 as a potent inhibitor of NOX1-derived O2⋅- formation, a panel of peptidomimetic derivatives of this peptide were designed and synthesized with the aim of improving their activity and increasing their stability in plasma. The results highlighted that improved efficacy and potency was found for both the peptide-peptoid hybrid GS2, whereas stapled peptide AC5 and its precursor showed higher stability despite lower biological potency. This study showed that minimal structural modifications of NOXA1 peptides are required to improve both their potency and stability to finally achieve best candidates as new potential anti-thrombotic drugs.

Fusarium graminearum effector FgEC1 targets wheat TaGF14b protein to suppress TaRBOHD-mediated ROS production and promote infection

Fusarium head blight (FHB), caused by Fusarium graminearum, is a devastating disease of wheat globally. However, the molecular mechanisms underlying the interactions between F. graminearum and wheat remain unclear. Here, we identified a secreted effector protein, FgEC1, that is induced during wheat infection and is required for F. graminearum virulence. FgEC1 suppressed flg22- and chitin-induced callose deposition and reactive oxygen species (ROS) burst in Nicotiana benthamiana. FgEC1 directly interacts with TaGF14b, which is upregulated in wheat heads during F. graminearum infection. Overexpression of TaGF14b increases FHB resistance in wheat without compromising yield. TaGF14b interacts with NADPH oxidase respiratory burst oxidase homolog D (TaRBOHD) and protects it against degradation by the 26S proteasome. FgEC1 inhibited the interaction of TaGF14b with TaRBOHD and promoted TaRBOHD degradation, thereby reducing TaRBOHD-mediated ROS production. Our findings reveal a novel pathogenic mechanism in which a fungal pathogen acts via an effector to reduce TaRBOHD-mediated ROS production.

Glucoraphanin and sulforaphane mitigate TNFα-induced Caco-2 monolayers permeabilization and inflammation

Intestinal permeabilization is central to the pathophysiology of chronic gut inflammation. This study investigated the efficacy of glucoraphanin (GR), prevalent in cruciferous vegetables, particularly broccoli, and its derivative sulforaphane (SF), in inhibiting tumor necrosis factor alpha (TNFα)-induced Caco-2 cell monolayers inflammation and permeabilization through the regulation of redox-sensitive events. TNFα binding to its receptor led to a rapid increase in oxidant production and subsequent elevation in the mRNA levels of NOX1, NOX4, and Duox2. GR and SF dose-dependently mitigated both these short- and long-term alterations in redox homeostasis. Downstream, GR and SF inhibited the activation of the redox-sensitive signaling cascades NF-κB (p65 and IKK) and MAPK ERK1/2, which contribute to inflammation and barrier permeabilization. GR (1 μM) and SF (0.5-1 μM) prevented TNFα-induced monolayer permeabilization and the associated reduction in the levels of the tight junction (TJ) proteins occludin and ZO-1. Both GR and SF also mitigated TNFα-induced increased mRNA levels of the myosin light chain kinase, which promotes TJ opening. Molecular docking suggests that although GR is mostly not absorbed, it could interact with extracellular and membrane sites in NOX1. Inhibition of NOX1 activity by GR would mitigate TNFα receptor downstream signaling and associated events. These findings support the concept that not only SF, but also GR, could exert systemic health benefits by protecting the intestinal barrier against inflammation-induced permeabilization, in part by regulating redox-sensitive pathways. GR has heretofore not been viewed as a biologically active molecule, but rather, the benign precursor of highly active SF. The consumption of GR and/or SF-rich vegetables or supplements in the diet may offer a means to mitigate the detrimental consequences of intestinal permeabilization, not only in disease states but also in conditions characterized by chronic inflammation of dietary and lifestyle origin.

Role of NOX1 and NOX5 in protein kinase C/reactive oxygen species‑mediated MMP‑9 activation and invasion in MCF‑7 breast cancer cells

NADPH oxidases (NOXs) are a family of membrane proteins responsible for intracellular reactive oxygen species (ROS) generation by facilitating electron transfer across biological membranes. Despite the established activation of NOXs by protein kinase C (PKC), the precise mechanism through which PKC triggers NOX activation during breast cancer invasion remains unclear. The present study aimed to investigate the role of NOX1 and NOX5 in the invasion of MCF‑7 human breast cancer cells. The expression and activity of NOXs and matrix metalloprotease (MMP)‑9 were assessed by reverse transcription‑quantitative PCR and western blotting, and the activity of MMP‑9 was monitored using zymography. Cellular invasion was assessed using the Matrigel invasion assay, whereas ROS levels were quantified using a FACSCalibur flow cytometer. The findings suggested that NOX1 and NOX5 serve crucial roles in 12‑O‑tetradecanoylphorbol‑13‑acetate (TPA)‑induced MMP‑9 expression and invasion of MCF‑7 cells. Furthermore, a connection was established between PKC and the NOX1 and 5/ROS signaling pathways in mediating TPA‑induced MMP‑9 expression and cellular invasion. Notably, NOX inhibitors (diphenyleneiodonium chloride and apocynin) significantly attenuated TPA‑induced MMP‑9 expression and invasion in MCF‑7 cells. NOX1‑ and NOX5‑specific small interfering RNAs attenuated TPA‑induced MMP‑9 expression and cellular invasion. In addition, knockdown of NOX1 and NOX5 suppressed TPA‑induced ROS levels. Furthermore, a PKC inhibitor (GF109203X) suppressed TPA‑induced intracellular ROS levels, MMP‑9 expression and NOX activity in MCF‑7 cells. Therefore, NOX1 and NOX5 may serve crucial roles in TPA‑induced MMP‑9 expression and invasion of MCF‑7 breast cancer cells. Furthermore, the present study indicated that TPA‑induced MMP‑9 expression and cellular invasion were mediated through PKC, thus linking the NOX1 and 5/ROS signaling pathways. These findings offer novel insights into the potential mechanisms underlying their anti‑invasive effects in breast cancer.

Tumor necrosis factor alpha induces NOX2-dependent reactive oxygen species production in hypothalamic paraventricular nucleus neurons following angiotensin II infusion

There is evidence that tumor necrosis factor alpha (TNFα) influences autonomic processes coordinated within the hypothalamic paraventricular nucleus (PVN), however, the signaling mechanisms subserving TNFα's actions in this brain area are unclear. In non-neuronal cell types, TNFα has been shown to play an important role in canonical NADPH oxidase (NOX2)-mediated production of reactive oxygen species (ROS), molecules also known to be critically involved in hypertension. However, little is known about the role of TNFα in NOX2-dependent ROS production in the PVN within the context of hypertension. Using dual labeling immunoelectron microscopy and dihydroethidium (DHE) microfluorography, we provide structural and functional evidence for interactions between TNFα and NOX2 in the PVN. The TNFα type 1 receptor (TNFR1), the major mediator of TNFα signaling in the PVN, was commonly co-localized with the catalytic gp91phox subunit of NOX2 in postsynaptic sites of PVN neurons. Additionally, there was an increase in dual labeled dendritic profiles following fourteen-day slow-pressor angiotensin II (AngII) infusion. Using DHE microfluorography, it was also shown that TNFα application resulted in a NOX2-dependent increase in ROS in isolated PVN neurons projecting to the spinal cord. Further, TNFα-mediated ROS production was heightened after AngII infusion. The finding that TNFR1 and gp91phox are positioned for rapid interactions, particularly in PVN-spinal cord projection neurons, provides a molecular substrate by which inflammatory signaling and oxidative stress may jointly contribute to AngII hypertension.

Very low-density lipoprotein receptor mediates triglyceride-rich lipoprotein-induced oxidative stress and insulin resistance

Obesity is associated with excess lipid deposition in nonadipose tissues, leading to increased oxidative stress and insulin resistance. Very low-density lipoprotein receptor (VLDLR), a member of the LDL receptor family, binds and increases the catabolism of triglyceride-rich lipoproteins. Although VLDLR is highly expressed in the heart, its role in obesity-associated oxidative stress and insulin resistance is unclear. Here, we used lean (wild type), genetically obese leptin-deficient (ob/ob), and leptin-VLDLR double-null (ob/ob-VLDLR-/-) mice to determine the impact of VLDLR deficiency on obesity-induced oxidative stress and insulin resistance in the heart. Although insulin sensitivity and glucose uptake were reduced in the hearts of ob/ob mice, VLDLR expression was upregulated and was associated with increased VLDL uptake and excess lipid deposition. This was accompanied by an upregulation of cardiac NADPH oxidase (Nox) expression and increased production of Nox-dependent superoxides. Silencing the VLDLR in ob/ob mice had reduced VLDL uptake and prevented excess lipid deposition in the heart, in addition to a reduction of superoxide overproduction and the normalization of insulin sensitivity and glucose uptake. In isolated cardiomyocytes, VLDLR deficiency had prevented VLDL-mediated induction of Nox activity and superoxide overproduction while improving insulin sensitivity and glucose uptake. Our findings indicate that VLDLR deficiency prevents excess lipid accumulation and moderates oxidative stress and insulin resistance in the hearts of obese mice. This effect is linked to the active role of VLDLR in VLDL uptake, which triggers a cascade of events leading to increased Nox activity, superoxide overproduction, and insulin resistance.NEW & NOTEWORTHY Obesity is associated with excess lipid deposition in muscles, which is considered as a leading cause of metabolic dysfunction and oxidative stress. Cellular uptake of lipids is regulated by several membrane receptors, among which is the very low-density lipoprotein receptor (VLDLR). This article provides information on the role of VLDLR in cardiac muscle and how its expression regulates insulin resistance and oxidative stress in the obese mouse model.

The NADPH oxidases DUOX1 and DUOX2 are sorted to the apical plasma membrane in epithelial cells via their respective maturation factors DUOXA1 and DUOXA2

The membrane-integrated NADPH oxidases DUOX1 and DUOX2 are recruited to the apical plasma membrane in epithelial cells to release hydrogen peroxide, thereby playing crucial roles in various functions such as thyroid hormone synthesis and host defense. However, it has remained unknown about the molecular mechanism for apical sorting of DUOX1 and DUOX2. Here we show that DUOX1 and DUOX2 are correctly sorted to the apical membrane via the membrane-spanning DUOX maturation proteins DUOXA1 and DUOXA2, respectively, when co-expressed in MDCK epithelial cells. Impairment of N-glycosylation of DUOXA1 results in mistargeting of DUOX1 to the basolateral membrane. Similar to DUOX1 complexed with the glycosylation-defective DUOXA1, the naturally non-glycosylated oxidase NOX5, which forms a homo-oligomer, is targeted basolaterally. On the other hand, a mutant DUOXA2 deficient in N-glycosylation is less stable than the wild-type protein but still capable of recruiting DUOX2 to the apical membrane, whereas DUOX2 is missorted to the basolateral membrane when paired with DUOXA1. These findings indicate that DUOXA2 is crucial but its N-glycosylation is dispensable for DUOX2 apical recruitment; instead, its C-terminal region seems to be involved. Thus, apical sorting of DUOX1 and DUOX2 is likely regulated in a distinct manner by their respective partners DUOXA1 and DUOXA2.

NADPH oxidases in healthy white adipose tissue and in obesity: function, regulation, and clinical implications

Reactive oxygen species, when produced in a controlled manner, are physiological modulators of healthy white adipose tissue (WAT) expansion and metabolic function. By contrast, unbridled production of oxidants is associated with pathological WAT expansion and the establishment of metabolic dysfunctions, most notably insulin resistance and type 2 diabetes mellitus. NADPH oxidases (NOXs) produce oxidants in an orderly fashion and are present in adipocytes and in other diverse WAT-constituent cell types. Recent studies have established several links between aberrant NOX-derived oxidant production, adiposity, and metabolic homeostasis. The objective of this review is to highlight the physiological roles attributed to diverse NOX isoforms in healthy WAT and summarize current knowledge of the metabolic consequences related to perturbations in their adequate oxidant production. We detail WAT-related alterations in preclinical investigations conducted in NOX-deficient murine models. In addition, we review clinical studies that have employed NOX inhibitors and currently available data related to human NOX mutations in metabolic disturbances. Future investigations aimed at understanding the integration of NOX-derived oxidants in the regulation of the WAT cellular redox network are essential for designing successful redox-related precision therapies to curb obesity and attenuate obesity-associated metabolic pathologies.

H2O2 sulfenylates CHE, linking local infection to the establishment of systemic acquired resistance

In plants, a local infection can lead to systemic acquired resistance (SAR) through increased production of salicylic acid (SA). For many years, the identity of the mobile signal and its direct transduction mechanism for systemic SA synthesis in initiating SAR have been debated. We found that in Arabidopsis thaliana, after a local infection, the conserved cysteine residue of the transcription factor CCA1 HIKING EXPEDITION (CHE) undergoes sulfenylation in systemic tissues, which enhances its binding to the promoter of the SA-synthesis gene ISOCHORISMATE SYNTHASE1 (ICS1) and increases SA production. Furthermore, hydrogen peroxide (H2O2) produced through NADPH oxidases is the mobile signal that sulfenylates CHE in a concentration-dependent manner. Accumulation of SA and the previously reported signal molecules, such as N-hydroxypipecolic acid (NHP), then form a signal amplification loop to establish SAR.

Glucose-Dependent Insulinotropic Polypeptide Inhibits AGE-Induced NADPH Oxidase-Derived Oxidative Stress Generation and Foam Cell Formation in Macrophages Partly via AMPK Activation

Glucose-dependent insulinotropic polypeptide (GIP) of the incretin group has been shown to exert pleiotropic actions. There is growing evidence that advanced glycation end products (AGEs), senescent macromolecules formed at an accelerated rate under chronic hyperglycemic conditions, play a role in the pathogenesis of atherosclerotic cardiovascular disease in diabetes. However, whether and how GIP could inhibit the AGE-induced foam cell formation of macrophages, an initial step of atherosclerosis remains to be elucidated. In this study, we address these issues. We found that AGEs increased oxidized low-density-lipoprotein uptake into reactive oxygen species (ROS) generation and Cdk5 and CD36 gene expressions in human U937 macrophages, all of which were significantly blocked by [D-Ala2]GIP(1-42) or an inhibitor of NADPH oxidase activity. An inhibitor of AMP-activated protein kinase (AMPK) attenuated all of the beneficial effects of [D-Ala2]GIP(1-42) on AGE-exposed U937 macrophages, whereas an activator of AMPK mimicked the effects of [D-Ala2]GIP(1-42) on foam cell formation, ROS generation, and Cdk5 and CD36 gene expressions in macrophages. The present study suggests that [D-Ala2]GIP(1-42) could inhibit the AGE-RAGE-induced, NADPH oxidase-derived oxidative stress generation in U937 macrophages via AMPK activation and subsequently suppress macrophage foam cell formation by reducing the Cdk5-CD36 pathway.

Complement-Mediated Two-Step NETosis: Serum-Induced Complement Activation and Calcium Influx Generate NADPH Oxidase-Dependent NETs in Serum-Free Conditions

The complement system and neutrophils play crucial roles in innate immunity. Neutrophils release neutrophil extracellular traps (NETs), which are composed of decondensed DNA entangled with granular contents, as part of their innate immune function. Mechanisms governing complement-mediated NET formation remain unclear. In this study, we tested a two-step NETosis mechanism, as follows: classical complement-mediated neutrophil activation in serum and subsequent NET formation in serum-free conditions, using neutrophils from healthy donors, endothelial cells, and various assays (Fluo-4AM, DHR123, and SYTOX), along with flow cytometry and confocal microscopy. Our findings reveal that classical complement activation on neutrophils upregulated the membrane-anchored complement regulators CD46, CD55, and CD59. Additionally, complement activation increased CD11b on neutrophils, signifying activation and promoting their attachment to endothelial cells. Complement activation induced calcium influx and citrullination of histone 3 (CitH3) in neutrophils. However, CitH3 formation alone was insufficient for NET generation. Importantly, NET formation occurred only when neutrophils were in serum-free conditions. In such environments, neutrophils induced NADPH oxidase-dependent reactive oxygen species (ROS) production, leading to NET formation. Hence, we propose that complement-mediated NET formation involves a two-step process, as follows: complement deposition, neutrophil priming, calcium influx, CitH3 formation, and attachment to endothelial cells in serum. This is followed by NADPH-dependent ROS production and NET completion in serum-free conditions. Understanding this process may unveil treatment targets for pathologies involving complement activation and NET formation.

The calcium-dependent protein kinase CPK16 regulates hypoxia-induced ROS production by phosphorylating the NADPH oxidase RBOHD in Arabidopsis

Reactive oxygen species (ROS) production is a key event in modulating plant responses to hypoxia and post-hypoxia reoxygenation. However, the molecular mechanism by which hypoxia-associated ROS homeostasis is controlled remains largely unknown. Here, we showed that the calcium-dependent protein kinase CPK16 regulates plant hypoxia tolerance by phosphorylating the plasma membrane-anchored NADPH oxidase respiratory burst oxidase homolog D (RBOHD) to regulate ROS production in Arabidopsis (Arabidopsis thaliana). In response to hypoxia or reoxygenation, CPK16 was activated through phosphorylation of its Ser274 residue. The cpk16 knockout mutant displayed enhanced hypoxia tolerance, whereas CPK16-overexpressing (CPK16-OE) lines showed increased sensitivity to hypoxic stress. In agreement with these observations, hypoxia and reoxygenation both induced ROS accumulation in the rosettes of CPK16-OEs more strongly than in the rosettes of the cpk16-1 mutant or the wild type. Moreover, CPK16 interacted with and phosphorylated the N-terminus of RBOHD at 4 serine residues (Ser133, Ser148, Ser163, and Ser347) that were necessary for hypoxia- and reoxygenation-induced ROS accumulation. Furthermore, the hypoxia-tolerant phenotype of cpk16-1 was fully abolished in the cpk16 rbohd double mutant. Thus, we have uncovered a regulatory mechanism by which the CPK16-RBOHD module shapes the ROS production during hypoxia and reoxygenation in Arabidopsis.

Activated factor X stimulates atrial endothelial cells and tissues to promote remodelling responses through AT1R/NADPH oxidases/SGLT1/2

AIMS

Atrial fibrillation (AF), the most common cardiac arrhythmia favouring ischemic stroke and heart failure involves left atrial remodelling, fibrosis and a complex interplay between cardiovascular risk factors. This study examined whether activated factor X (FXa) induces pro-remodelling and pro-fibrotic responses in atrial endothelial cells (AECs) and human atrial tissues and determined the underlying mechanisms.

METHODS AND RESULTS

AECs collected from porcine hearts and human right atrial appendages (RAA) from patients undergoing heart surgery. Protein expression levels were assessed by Western blot and immunofluorescence staining, mRNA levels by RT-qPCR, formation of reactive oxygen species (ROS) and NO using fluorescent probes, thrombin and angiotensin II generation by specific assays, fibrosis by Sirius red staining and senescence by senescence-associated beta-galactosidase (SA-β-gal) activity. In AECs, FXa increased ROS formation, senescence (SA-β-gal activity, p53, p21), angiotensin II generation and the expression of pro-inflammatory (VCAM-1, MCP-1), pro-thrombotic (tissue factor), pro-fibrotic (TGF-β and collagen-1/3a) and pro-remodelling (MMP-2/9) markers whereas eNOS levels and NO formation were reduced. These effects were prevented by inhibitors of FXa but not thrombin, protease-activated receptors antagonists (PAR-1/2) and inhibitors of NADPH oxidases, ACE, AT1R, SGLT1/SGLT2. FXa also increased expression levels of ACE1, AT1R, SGLT1/2 proteins which were prevented by SGLT1/2 inhibitors. Human RAA showed tissue factor mRNA levels that correlated with markers of endothelial activation, pro-remodelling and pro-fibrotic responses and SGLT1/2 mRNA levels. They also showed protein expression levels of ACE1, AT1R, p22phox, SGLT1/2, and immunofluorescence signals of nitrotyrosine and SGLT1/2 colocalized with those of CD31. FXa increased oxidative stress levels which were prevented by inhibitors of the AT1R/NADPH oxidases/SGLT1/2 pathway.

CONCLUSION

FXa promotes oxidative stress triggering premature endothelial senescence and dysfunction associated with pro-thrombotic, pro-remodelling and pro-fibrotic responses in AECs and human RAA involving the AT1R/NADPH oxidases/SGLT1/2 pro-oxidant pathway. Targeting this pathway may be of interest to prevent atrial remodelling and the progression of atrial fibrillation substrate.

Stretch-induced reactive oxygen species contribute to the Frank-Starling mechanism

Myocardial stretch physiologically activates NADPH oxidase 2 (NOX2) to increase reactive oxygen species (ROS) production. Although physiological low-level ROS are known to be important as signalling molecules, the role of stretch-induced ROS in the intact myocardium remains unclear. To address this, we investigated the effects of stretch-induced ROS on myocardial cellular contractility and calcium transients in C57BL/6J and NOX2-/- mice. Axial stretch was applied to the isolated cardiomyocytes using a pair of carbon fibres attached to both cell ends to evaluate stretch-induced modulation in the time course of the contraction curve and calcium transient, as well as to evaluate maximum cellular elastance, an index of cellular contractility, which is obtained from the end-systolic force-length relationship. In NOX2-/- mice, the peak calcium transient was not altered by stretch, as that in wild-type mice, but the lack of stretch-induced ROS delayed the rise of calcium transients and reduced contractility. Our mathematical modelling studies suggest that the augmented activation of ryanodine receptors by stretch-induced ROS causes a rapid and large increase in the calcium release flux, resulting in a faster rise in the calcium transient. The slight increase in the magnitude of calcium transients is offset by a decrease in sarcoplasmic reticulum calcium content as a result of ROS-induced calcium leakage, but the faster rise in calcium transients still maintains higher contractility. In conclusion, a physiological role of stretch-induced ROS is to increase contractility to counteract a given preload, that is, it contributes to the Frank-Starling law of the heart. KEY POINTS: Myocardial stretch increases the production of reactive oxygen species by NADPH oxidase 2. We used NADPH oxidase 2 knockout mice to elucidate the physiological role of stretch-induced reactive oxygen species in the heart. We showed that stretch-induced reactive oxygen species modulate the rising phase of calcium transients and increase myocardial contractility. A mathematical model simulation study demonstrated that rapid activation of ryanodine receptors by reactive oxygen species is important for increased contractility. This response is advantageous for the myocardium, which must contract against a given preload.

NADPH Oxidases in Neurodegenerative Disorders: Mechanisms and Therapeutic Opportunities

Significance: The nicotinamide adenine dinucleotide phosphate oxidase (NOX) enzyme family, located in the central nervous system, is recognized as a source of reactive oxygen species (ROS) in the brain. Despite its importance in cellular processes, excessive ROS generation leads to cell death and is involved in the pathogenesis of neurodegenerative disorders. Recent advances: NOX enzymes contribute to the development of neurodegenerative diseases, such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and stroke, highlighting their potential as targets for future therapeutic development. This review will discuss NOX's contribution and therapeutic targeting potential in neurodegenerative diseases, focusing on PD, AD, ALS, and stroke. Critical issues: Homeostatic and physiological levels of ROS are crucial for regulating several processes, such as development, memory, neuronal signaling, and vascular homeostasis. However, NOX-mediated excessive ROS generation is deeply involved in the damage of DNA, proteins, and lipids, leading to cell death in the pathogenesis of a wide range of diseases, namely neurodegenerative diseases. Future directions: It is essential to understand the role of NOX homologs in neurodegenerative disorders and the pathological mechanisms undergoing neurodegeneration mediated by increased levels of ROS. This further knowledge will allow the development of new specific NOX inhibitors and their application for neurodegenerative disease therapeutics. Antioxid. Redox Signal. 41, 522-541.

Chemerin in caudal division of nucleus tractus solitarius increases sympathetic activity and blood pressure

Chemerin is an adipokine that contributes to metabolism regulation. Nucleus tractus solitarius (NTS) is the first relay station in the brain for accepting various visceral afferent activities for regulating cardiovascular activity. However, the roles of chemerin in the NTS in regulating sympathetic activity and blood pressure are almost unknown. This study aimed to determine the role and potential mechanism of chemerin in the NTS in modulating sympathetic outflow and blood pressure. Bilateral NTS microinjections were performed in anaesthetized adult male Sprague-Dawley rats. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were continuously recorded. Chemerin and its receptor chemokine-like receptor 1 (CMKLR1) were highly expressed in caudal NTS (cNTS). Microinjection of chemerin-9 to the cNTS increased RSNA, MAP and HR, which were prevented by CMKLR1 antagonist α-NETA, superoxide scavenger tempol or N-acetyl cysteine, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors diphenyleneiodonium or apocynin. Chemerin-9 increased superoxide production and NADPH oxidase activity in the cNTS. The increased superoxide production induced by chemerin-9 was inhibited by α-NETA. The effects of cNTS microinjection of chemerin-9 on the RSNA, MAP and HR were attenuated by the pretreatment with paraventricular nucleus (PVN) microinjection of NMDA receptor antagonist MK-801 rather than AMPA/kainate receptor antagonist CNQX. These results indicate that chemerin-9 in the NTS increases sympathetic outflow, blood pressure and HR via CMKLR1-mediated NADPH oxidase activation and subsequent superoxide production in anaesthetized normotensive rats. Glutamatergic inputs in the PVN are needed for the chemerin-9-induced responses.

NADPH Alters DUOX1 Calcium Responsiveness

Hydrogen peroxide is a key element in redox signaling and in setting cellular redox tone. DUOX1 and DUOX2, that directly synthesize hydrogen peroxide, are the most abundant NADPH oxidase transcripts in most epithelia. DUOX1 and DUOX2 hydrogen peroxide synthesis is regulated by intracellular calcium transients and thus cells can respond to signals and initiate responses by increasing cellular hydrogen peroxide synthesis. Nevertheless, many details of their enzymatic regulation are still unexplored. DUOX1 and DUOXA1 were expressed in HEK293T cells and activity was studied in homogenates and membrane fractions. When DUOX1 homogenates or membranes were pre-incubated in NADPH and started with addition of Ca2+, to mimic intracellular activation, progress curves were distinctly different from those pre-incubated in Ca2+ and started with NADPH. The Ca2+ EC50 for DUOX1's initial rate when pre-incubated in Ca2+, was three orders of magnitude lower (EC50 ∼ 10-6 M) than with preincubation in NADPH (EC50 ∼ 10-3 M). In addition, activity was several fold lower with Ca2+ start. Identical results were obtained using homogenates and membrane fractions. The data suggested that DUOX1 Ca2+ binding in expected physiological signaling conditions only slowly leads to maximal hydrogen peroxide synthesis and that full hydrogen peroxide synthesis activity in vivo only can occur when encountering extremely high concentration Ca2+ signals. Thus, a complex interplay of intracellular NADPH and Ca2+ concentrations regulate DUOX1 over a wide extent and may limit DUOX1 activity to a restricted range and spatial distribution.

Nuclear Localization of Human SOD1 in Motor Neurons in Mouse Model and Patient Amyotrophic Lateral Sclerosis: Possible Links to Cholinergic Phenotype, NADPH Oxidase, Oxidative Stress, and DNA Damage

Amyotrophic lateral sclerosis (ALS) is a fatal disease that causes degeneration of motor neurons (MNs) and paralysis. ALS can be caused by mutations in the gene that encodes copper/zinc superoxide dismutase (SOD1). SOD1 is known mostly as a cytosolic antioxidant protein, but SOD1 is also in the nucleus of non-transgenic (tg) and human SOD1 (hSOD1) tg mouse MNs. SOD1's nuclear presence in different cell types and subnuclear compartmentations are unknown, as are the nuclear functions of SOD1. We examined hSOD1 nuclear localization and DNA damage in tg mice expressing mutated and wildtype variants of hSOD1 (hSOD1-G93A and hSOD1-wildtype). We also studied ALS patient-derived induced pluripotent stem (iPS) cells to determine the nuclear presence of SOD1 in undifferentiated and differentiated MNs. In hSOD1-G93A and hSOD1-wildtype tg mice, choline acetyltransferase (ChAT)-positive MNs had nuclear hSOD1, but while hSOD1-wildtype mouse MNs also had nuclear ChAT, hSOD1-G93A mouse MNs showed symptom-related loss of nuclear ChAT. The interneurons had preserved parvalbumin nuclear positivity in hSOD1-G93A mice. hSOD1-G93A was seen less commonly in spinal cord astrocytes and, notably, oligodendrocytes, but as the disease emerged, the oligodendrocytes had increased mutant hSOD1 nuclear presence. Brain and spinal cord subcellular fractionation identified mutant hSOD1 in soluble nuclear extracts of the brain and spinal cord, but mutant hSOD1 was concentrated in the chromatin nuclear extract only in the spinal cord. Nuclear extracts from mutant hSOD1 tg mouse spinal cords had altered protein nitration, footprinting peroxynitrite presence, and the intact nuclear extracts had strongly increased superoxide production as well as the active NADPH oxidase marker, p47phox. The comet assay showed that MNs from hSOD1-G93A mice progressively (6-14 weeks of age) accumulated DNA single-strand breaks. Ablation of the NCF1 gene, encoding p47phox, and pharmacological inhibition of NADPH oxidase with systemic treatment of apocynin (10 mg/kg, ip) extended the mean lifespan of hSOD1-G93A mice by about 25% and mitigated genomic DNA damage progression. In human postmortem CNS, SOD1 was found in the nucleus of neurons and glia; nuclear SOD1 was increased in degenerating neurons in ALS cases and formed inclusions. Human iPS cells had nuclear SOD1 during directed differentiation to MNs, but mutant SOD1-expressing cells failed to establish wildtype MN nuclear SOD1 levels. We conclude that SOD1 has a prominent nuclear presence in the central nervous system, perhaps adopting aberrant contexts to participate in ALS pathobiology.

The peptidyl-prolyl isomerase Pin1 controls GM-CSF-induced priming of NADPH oxidase in human neutrophils and priming at inflammatory sites

The production of superoxide anions and other reactive oxygen species (ROS) by neutrophils is necessary for host defense against microbes. However, excessive ROS production can induce cell damage that participates in the inflammatory response. Superoxide anions are produced by the phagocyte NADPH oxidase, a multicomponent enzyme system consisting of two transmembrane proteins (gp91phox/NOX2 and p22phox) and four soluble cytosolic proteins (p40phox, p47phox, p67phox and the small G proteins Rac1/2). Stimulation of neutrophils by various agonists, such as the bacterial peptide formyl-Met-Leu-Phe (fMLF), induces NADPH oxidase activation and superoxide production, a process that is enhanced by the pro-inflammatory cytokines such as GM-CSF. The pathways involved in this GM-CSF-induced up-regulation or priming are not fully understood. Here we show that GM-CSF induces the activation of the prolyl cis/trans isomerase Pin1 in human neutrophils. Juglone and PiB, two selective Pin1 inhibitors, were able to block GM-CSF-induced priming of ROS production by human neutrophils. Interestingly, GM-CSF induced Pin1 binding to phosphorylated p47phox at Ser345. Neutrophils isolated from synovial fluid of patients with rheumatoid arthritis are known to be primed. Here we show that Pin1 activity was also increased in these neutrophils and that Pin1 inhibitors effectively inhibited ROS hyperproduction by the same cells. These results suggest that the prolyl cis/trans isomerase Pin1 may control GM-CSF-induced priming of ROS production by neutrophils and priming of neutrophils in synovial fluid of rheumatoid arthritis patients. Pharmacological targeting of Pin1 may be a valuable approach to the treatment of inflammation.

NADPH oxidase-mediated sulfenylation of cysteine derivatives regulates plant immunity

Reactive oxygen species (ROS) are rapidly generated during plant immune responses by respiratory burst oxidase homolog (RBOH), which is a plasma membrane-localized NADPH oxidase. Although regulatory mechanisms of RBOH activity have been well documented, the ROS-mediated downstream signaling is unclear. We here demonstrated that ROS sensor proteins play a central role in ROS signaling via oxidative post-translational modification of cysteine residues, sulfenylation. To detect protein sulfenylation, we used dimedone, which specifically and irreversibly binds to sulfenylated proteins. The sulfenylated proteins were labeled by dimedone in Nicotiana benthamiana leaves, and the conjugates were detected by immunoblot analyses. In addition, a reductant dissociated H2O2-induced conjugates, suggesting that cysteine persulfide and/or polysulfides are involved in sulfenylation. These sulfenylated proteins were continuously increased during both pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) in a RBOH-dependent manner. Pharmacological inhibition of ROS sensor proteins by dimedone perturbated cell death, ROS accumulation induced by INF1 and MEK2DD, and defense against fungal pathogens. On the other hand, Rpi-blb2-mediated ETI responses were enhanced by dimedone. These results suggest that the sulfenylation of cysteine and its derivatives in various ROS sensor proteins are important events downstream of the RBOH-dependent ROS burst to regulate plant immune responses.