Tyrosine cross-linking of extracellular matrix is catalyzed by Duox, a multidomain oxidase/peroxidase with homology to the phagocyte oxidase subunit gp91phox

A pathogenesis assay using Saccharomyces cerevisiae and Caenorhabditis elegans reveals novel roles for yeast AP-1, Yap1, and host dual oxidase BLI-3 in fungal pathogenesis

Treatment of systemic fungal infections is difficult because of the limited number of antimycotic drugs available. Thus, there is an immediate need for simple and innovative systems to assay the contribution of individual genes to fungal pathogenesis. We have developed a pathogenesis assay using Caenorhabditis elegans, an established model host, with Saccharomyces cerevisiae as the invading fungus. We have found that yeast infects nematodes, causing disease and death. Our data indicate that the host produces reactive oxygen species (ROS) in response to fungal infection. Yeast mutants sod1Delta and yap1Delta, which cannot withstand ROS, fail to cause disease, except in bli-3 worms, which carry a mutation in a dual oxidase gene. Chemical inhibition of the NADPH oxidase activity abolishes ROS production in worms exposed to yeast. This pathogenesis assay is useful for conducting systematic, whole-genome screens to identify fungal virulence factors as alternative targets for drug development and exploration of host responses to fungal infections.

Caenorhabditis elegans and human dual oxidase 1 (DUOX1) "peroxidase" domains: insights into heme binding and catalytic activity

The seven members of the NOX/DUOX family are responsible for generation of the superoxide and H(2)O(2) required for a variety of host defense and cell signaling functions in nonphagocytic cells. Two members, the dual oxidase isozymes DUOX1 and DUOX2, share a structurally unique feature: an N-terminal peroxidase-like domain. Despite sequence similarity to the mammalian peroxidases, the absence of key active site residues makes their binding of heme and their catalytic function uncertain. To explore this domain we have expressed in a baculovirus system and purified the Caenorhabditis elegans (CeDUOX1(1-589)) and human (hDUOX1(1-593)) DUOX1 "peroxidase" domains. Evaluation of these proteins demonstrated that the isolated hDUOX1(1-593) does not bind heme and has no intrinsic peroxidase activity. In contrast, CeDUOX1(1-589) binds heme covalently, exhibits a modest peroxidase activity, but does not oxidize bromide ion. Surprisingly, the heme appears to have two covalent links to the protein despite the absence of a second conserved carboxyl group in the active site. Although the N-terminal dual oxidase motif has been proposed to directly convert superoxide to H(2)O(2), neither DUOX1 domain demonstrated significant superoxide dismutase activity. These results strengthen the in vivo conclusion that the CeDUOX1 protein supports controlled peroxidative polymerization of tyrosine residues and indicate that the hDUOX1 protein either has a unique function or must interact with other protein factors to express its catalytic activity.

Isoforms and functions of NAD(P)H oxidase at the macula densa

Macula densa cells produce superoxide (O2-) during tubuloglomerular feedback primarily via NAD(P)H oxidase (NOX). The purpose of the present study was to determine NOXs expressed by the macula densa and the role of each one in NaCl-induced O2- production. To identify which isoforms are expressed, we applied single-cell RT-PCR to macula densa cells isolated by laser capture microdissection and to MMDD1 cells (a macula densa-like cell line). The captured cells expressed neuronal NOS (marker of macula densa), NOX2, and NOX4 but not NOX1. Expression of the NOXs and neuronal NOS was essentially identical in the MMDD1 cells. Thus, we used MMDD1 cells to investigate which isoform is responsible for NaCl-induced O2- production. We used small-interfering RNA to knock down NOX2 or NOX4 in MMDD1 cells and measured O2- exposed to low-salt solution (LS; 70 mmol/L of NaCl) or high-salt solution (HS; 140 mmol/L of NaCl). Exposing control cells (scrambled small-interfering RNA) to HS increased O2- concentrations from 0.75+/-0.28 to 1.48+/-0.46 U/min per 10(5) cells in LS and HS, respectively (P<0.001). Inhibiting NOX2 blocked the HS-induced increase in O2- (0.62+/-0.39 versus 0.76+/-0.31 U/min per 10(5) cells in LS and HS groups, respectively). Blocking NOX4 did not affect HS-induced O2- levels. O2- levels in the control cells during LS and HS were 0.80+/-0.30 and 1.56+/-0.49 U/min per 10(5) cells, respectively (P<0.001); whereas O2- levels in NOX4-small-interfering RNA-treated cells during LS and HS were 0.40+/-0.25 and 1.26+/-0.51 U/min per 10(5) cells, respectively (P<0.001). We conclude that, whereas macula densa cells express the NOX2 and NOX4 isoforms, NOX2 is primarily responsible for NaCl-induced O2- generation.

Identification and characterization of VPO1, a new animal heme-containing peroxidase

Animal heme-containing peroxidases play roles in innate immunity, hormone biosynthesis, and the pathogenesis of inflammatory diseases. Using the peroxidase-like domain of Duox1 as a query, we carried out homology searching of the National Center for Biotechnology Information database. Two novel heme-containing peroxidases were identified in humans and mice. One, termed VPO1 for vascular peroxidase 1, exhibits its highest tissue expression in heart and vascular wall. A second, VPO2, present in humans but not in mice, is 63% identical to VPO1 and is highly expressed in heart. The peroxidase homology region of VPO1 shows 42% identity to myeloperoxidase and 57% identity to the insect peroxidase peroxidasin. A molecular model of the VPO1 peroxidase region reveals a structure very similar to that of known peroxidases, including a conserved heme binding cavity, critical catalytic residues, and a calcium binding site. The absorbance spectra of VPO1 are similar to those of lactoperoxidase, and covalent attachment of the heme to VPO1 protein was demonstrated by chemiluminescent heme staining. VPO1 purified from heart or expressed in HEK cells is catalytically active, with a K(m) for H(2)O(2) of 1.5 mM. When co-expressed in cells, VPO1 can use H(2)O(2) produced by NADPH oxidase enzymes. VPO1 is likely to carry out peroxidative reactions previously attributed exclusively to myeloperoxidase in the vascular system.

Duox maturation factors form cell surface complexes with Duox affecting the specificity of reactive oxygen species generation

Dual oxidases (Duox1 and Duox2) are plasma membrane-targeted hydrogen peroxide generators that support extracellular hemoperoxidases. Duox activator 2 (Duoxa2), initially described as an endoplasmic reticulum resident protein, functions as a maturation factor needed to deliver active Duox2 to the cell surface. However, less is known about the Duox1/Duoxa1 homologues. We identified four alternatively spliced Duoxa1 variants and explored their roles in Duox subcellular targeting and reconstitution. Duox1 and Duox2 are functionally rescued by Duoxa2 or the Duoxa1 variants that contain the third coding exon. All active maturation factors are cotransported to the cell surface when coexpressed with either Duox1 or Duox2, consistent with detection of endogenous Duoxa1 on apical plasma membranes of the airway epithelium. In contrast, the Duoxa proteins are retained in the endoplasmic reticulum when expressed without Duox. Duox1/Duoxa1alpha and Duox2/Duoxa2 pairs produce the highest levels of hydrogen peroxide, as they undergo Golgi-based carbohydrate modifications and form stable cell surface complexes. Cross-functioning pairs that do not form stable complexes produce less hydrogen peroxide and leak superoxide. These findings suggest Duox activators not only promote Duox maturation, but they function as part of the hydrogen peroxide-generating enzyme.

The Caenorhabditis elegans rsd-2 and rsd-6 genes are required for chromosome functions during exposure to unfavorable environments

In Caenorhabditis elegans, exogenous dsRNA can elicit systemic RNAi, a process that requires the function of many genes. Considering that the activities of many of these genes are also required for normal development, it is surprising that exposure to high concentrations of dsRNA does not elicit adverse consequences to animals. Here, we report inducible phenotypes in attenuated C. elegans strains reared in environments that include nonspecific dsRNA and elevated temperature. Under these conditions, chromosome integrity is compromised in RNAi-defective strains harboring mutations in rsd-2 or rsd-6. Specifically, rsd-2 mutants display defects in transposon silencing, while meiotic chromosome disjunction is affected in rsd-6 mutants. RSD-2 proteins localize to multiple cellular compartments, including the nucleolus and cytoplasmic compartments that, in part, are congruent with calreticulin and HAF-6. We considered that the RNAi defects in rsd-2 mutants might have relevance to membrane-associated functions; however, endomembrane compartmentalization and endocytosis/exocytosis markers in rsd-2 and rsd-6 mutants appear normal. The mutants also possess environmentally sensitive defects in cell-autonomous RNAi elicited from transgene-delivered dsRNAs. Thus, the ultimate functions of rsd-2 and rsd-6 in systemic RNAi are remarkably complex and environmentally responsive.

Structure, regulation and evolution of Nox-family NADPH oxidases that produce reactive oxygen species

NADPH oxidases of the Nox family exist in various supergroups of eukaryotes but not in prokaryotes, and play crucial roles in a variety of biological processes, such as host defense, signal transduction, and hormone synthesis. In conjunction with NADPH oxidation, Nox enzymes reduce molecular oxygen to superoxide as a primary product, and this is further converted to various reactive oxygen species. The electron-transferring system in Nox is composed of the C-terminal cytoplasmic region homologous to the prokaryotic (and organelle) enzyme ferredoxin reductase and the N-terminal six transmembrane segments containing two hemes, a structure similar to that of cytochrome b of the mitochondrial bc(1) complex. During the course of eukaryote evolution, Nox enzymes have developed regulatory mechanisms, depending on their functions, by inserting a regulatory domain (or motif) into their own sequences or by obtaining a tightly associated protein as a regulatory subunit. For example, one to four Ca(2+)-binding EF-hand motifs are present at the N-termini in several subfamilies, such as the respiratory burst oxidase homolog (Rboh) subfamily in land plants (the supergroup Plantae), the NoxC subfamily in social amoebae (the Amoebozoa), and the Nox5 and dual oxidase (Duox) subfamilies in animals (the Opisthokonta), whereas an SH3 domain is inserted into the ferredoxin-NADP(+) reductase region of two Nox enzymes in Naegleria gruberi, a unicellular organism that belongs to the supergroup Excavata. Members of the Nox1-4 subfamily in animals form a stable heterodimer with the membrane protein p22(phox), which functions as a docking site for the SH3 domain-containing regulatory proteins p47(phox), p67(phox), and p40(phox); the small GTPase Rac binds to p67(phox) (or its homologous protein), which serves as a switch for Nox activation. Similarly, Rac activates the fungal NoxA via binding to the p67(phox)-like protein Nox regulator (NoxR). In plants, on the other hand, this GTPase directly interacts with the N-terminus of Rboh, leading to superoxide production. Here I describe the regulation of Nox-family oxidases on the basis of three-dimensional structures and evolutionary conservation.

Anabolic function of phenylalanine hydroxylase in Caenorhabditis elegans

In humans, liver phenylalanine hydroxylase (PAH) has an established catabolic function, and mutations in PAH cause phenylketonuria, a genetic disease characterized by neurological damage, if not treated. To obtain novel evolutionary insights and information on molecular mechanisms operating in phenylketonuria, we investigated PAH in the nematode Caenorhabditis elegans (cePAH), where the enzyme is coded by the pah-1 gene, expressed in the hypodermis. CePAH presents similar molecular and kinetic properties to human PAH [S(0.5)(L-Phe) approximately 150 microM; K(m) for tetrahydrobiopterin (BH(4)) approximately 35 microM and comparable V(max)], but cePAH is devoid of positive cooperativity for L-Phe, an important regulatory mechanism of mammalian PAH that protects the nervous system from excess L-Phe. Pah-1 knockout worms show no obvious neurological defects, but in combination with a second cuticle synthesis mutation, they display serious cuticle abnormalities. We found that pah-1 knockouts lack a yellow-orange pigment in the cuticle, identified as melanin by spectroscopic techniques, and which is detected in C. elegans for the first time. Pah-1 mutants show stimulation of superoxide dismutase activity, suggesting that cuticle melanin functions as oxygen radical scavenger. Our results uncover both an important anabolic function of PAH and the change in regulation of the enzyme along evolution.

A novel homozygous missense mutation of the dual oxidase 2 (DUOX2) gene in an adult patient with large goiter

OBJECTIVE

To describe the first adult case of large goiter associated with a novel R1110Q mutation in the dual oxidase 2 (DUOX2) gene. She was initially euthyroid, and developed hypothyroidism later in her forties. DUOX2 is an essential enzyme in iodine organification of thyroid hormone biosynthesis. Only infant cases of congenital hypothyroidism due to mutations of the DUOX2 gene have been reported. Biallelic mutation of DUOX2 is thought to lead to total iodine organification defect. PATIENTS AND MEASUREMENT: This 57-year-old woman became first aware of goiter around the age of 20 years. Since the goiter had enlarged gradually, she consulted us at the age of 32 years. Goiter was soft, and thyroid function was normal. Antithyroid antibodies were negative. Both physical and mental development was normal. Three of her nine siblings and her mother had large goiters. At the age of 44 years, thyroid function demonstrated subclinical hypothyroidism. She started to take levo-thyroxine at a dose of 100 mug/day to reduce goiter. At the age of 56 years, goiter size remained the same. The perchlorate discharge rate was 72.8%, suggesting partial iodine organification defect. Thus, thyroid peroxidase (TPO) gene and DUOX2 gene were analyzed.

RESULTS

There was no mutation in the TPO gene, but a novel homozygous mutation (R1110Q) in the DUOX2 gene was identified. The same heterozygous mutation was detected in her two sons and two grandchildren. This mutation was not detected in 104 control alleles and was located at a site differing from any other reported mutations in the DUOX2 gene.

CONCLUSIONS

This homozygous missense mutation can be associated with thyroid dysfunction and goiter formation of an enlarged thyroid gland.

NADPH oxidases in lung biology and pathology: host defense enzymes, and more

The deliberate production of reactive oxygen species (ROS) by phagocyte NADPH oxidase is widely appreciated as a critical component of antimicrobial host defense. Recently, additional homologs of NADPH oxidase (NOX) have been discovered throughout the animal and plant kingdoms, which appear to possess diverse functions in addition to host defense, in cell proliferation, differentiation, and in regulation of gene expression. Several of these NOX homologs are also expressed within the respiratory tract, where they participate in innate host defense as well as in epithelial and inflammatory cell signaling and gene expression, and fibroblast and smooth muscle cell proliferation, in response to bacterial or viral infection and environmental stress. Inappropriate expression or activation of NOX/DUOX during various lung pathologies suggests their specific involvement in respiratory disease. This review summarizes the current state of knowledge regarding the general functional properties of mammalian NOX enzymes, and their specific importance in respiratory tract physiology and pathology.

Free-radical crosslinking of specific proteins alters the function of the egg extracellular matrix at fertilization

All animal embryos begin development by modifying the egg extracellular matrix. This protein-rich matrix protects against polyspermy, microbes and mechanical stress via enzyme-dependent transformations that alter the organization of its constituents. Using the sea urchin fertilization envelope,a well-defined extracellular structure formed within minutes of fertilization,we examine the mechanisms whereby limited permeability is established within this matrix. We find that the fertilization envelope acquires a barrier filtration of 40,000 daltons within minutes of insemination via a peroxidase-dependent mechanism, with dynamics that parallel requisite production of hydrogen peroxide by the zygote. To identify the molecular targets of this free-radical modification, we developed an in vivo technique to label and isolate the modified matrix components for mass spectrometry. This method revealed that four of the six major extracellular matrix components are selectively crosslinked, discriminating even sibling proteins from the same gene. Thus, specific free-radical chemistry is essential for establishing the embryonic microenvironment of early development.

Caenorhabditis elegans ABCRNAi transporters interact genetically with rde-2 and mut-7

RNA interference (RNAi) mechanisms are conserved and consist of an interrelated network of activities that not only respond to exogenous dsRNA, but also perform endogenous functions required in the fine tuning of gene expression and in maintaining genome integrity. Not surprisingly, RNAi functions have widespread influences on cellular function and organismal development. Previously, we observed a reduced capacity to mount an RNAi response in nine Caenorhabditis elegans mutants that are defective in ABC transporter genes (ABC(RNAi) mutants). Here, we report an exhaustive study of mutants, collectively defective in 49 different ABC transporter genes, that allowed for the categorization of one additional transporter into the ABC(RNAi) gene class. Genetic complementation tests reveal functions for ABC(RNAi) transporters in the mut-7/rde-2 branch of the RNAi pathway. These second-site noncomplementation interactions suggest that ABC(RNAi) proteins and MUT-7/RDE-2 function together in parallel pathways and/or as multiprotein complexes. Like mut-7 and rde-2, some ABC(RNAi) mutants display transposon silencing defects. Finally, our analyses reveal a genetic interaction network of ABC(RNAi) gene function with respect to this part of the RNAi pathway. From our results, we speculate that the coordinated activities of ABC(RNAi) transporters, through their effects on endogenous RNAi-related mechanisms, ultimately affect chromosome function and integrity.

The Role of DUOX Isozymes in the Respiratory Tract Epithelium

Increasingly, reactive oxygen species such as superoxide and hydrogen peroxide are recognized to be intentionally generated intracellularly to serve important cellular functions. A key protein family responsible for the regulated generation of reactive oxygen species in multiple cell types is the NOX/DUOX enzyme family. Two family members, DUOX1 and DUOX2, appear to be highly expressed in tissues of endodermal origin including the thyroid, respiratory tract, and gastrointestinal tract. In this chapter, we will focus our review on DUOX proteins in the respiratory tract. We will discuss a brief history of the discovery of the DUOX isoforms, the estimated hydrogen peroxide-generating capacity of DUOX in respiratory tract epithelium, putative functions of the DUOX enzymes, and some regulatory factors responsible for DUOX gene expression and oxidase activity.

The function of the NADPH oxidase of phagocytes, and its relationship to other NOXs

The NADPH oxidase of ‘professional’ phagocytic cells transfers electrons across the wall of the phagocytic vacuole, forming superoxide in the lumen. It is generally accepted that this system promotes microbial killing through the generation of reactive oxygen species and through the activity of myeloperoxidase. An alternative scenario exists in which the passage of electrons across the membrane alters the pH and generates a charge that drives ions into, and out of, the vacuole. It is proposed that the primary function of the oxidase is to produce these pH changes and ion fluxes, and the issues surrounding these processes are considered in this review. The neutrophil oxidase is the prototype of a whole family of NOXs (NAPDH oxidases) that exist throughout biology, from plants to humans, which might function, at least in part, in a similar fashion.

The function of the NADPH oxidase of phagocytes and its relationship to other NOXs in plants, invertebrates, and mammals

The NADPH (nicotinamide adenine dinucleotide phosphate) oxidase (NOX) of ‘professional’ phagocytic cells transfers electrons across the wall of the phagocytic vacuole, forming superoxide in the lumen. It is generally accepted that this system promotes microbial killing through the generation of reactive oxygen species and through the activity of myeloperoxidase. An alternative scenario exists in which the passage of electrons across the membrane alters the pH and generates a charge that drives ions into, and out of, the vacuole. It is proposed that the primary function of the oxidase is to produce these pH changes and ion fluxes, and the issues surrounding these processes are considered. The neutrophil oxidase is the prototype of a whole family of NOXs that exist throughout biology, from plants to man, which might function, at least in part, in a similar fashion. Some examples of how these other NOXs might influence ion fluxes are examined.

Molecular evolution of Phox-related regulatory subunits for NADPH oxidase enzymes

Background

The reactive oxygen-generating NADPH oxidases (Noxes) function in a variety of biological roles, and can be broadly classified into those that are regulated by subunit interactions and those that are regulated by calcium. The prototypical subunit-regulated Nox, Nox2, is the membrane-associated catalytic subunit of the phagocyte NADPH-oxidase. Nox2 forms a heterodimer with the integral membrane protein, p22phox, and this heterodimer binds to the regulatory subunits p47phox, p67phox, p40phox and the small GTPase Rac, triggering superoxide generation. Nox-organizer protein 1 (NOXO1) and Nox-activator 1 (NOXA1), respective homologs of p47phox and p67phox, together with p22phox and Rac, activate Nox1, a non-phagocytic homolog of Nox2. NOXO1 and p22phox also regulate Nox3, whereas Nox4 requires only p22phox. In this study, we have assembled and analyzed amino acid sequences of Nox regulatory subunit orthologs from vertebrates, a urochordate, an echinoderm, a mollusc, a cnidarian, a choanoflagellate, fungi and a slime mold amoeba to investigate the evolutionary history of these subunits.

Results

Ancestral p47phox, p67phox, and p22phox genes are broadly seen in the metazoa, except for the ecdysozoans. The choanoflagellate Monosiga brevicollis, the unicellular organism that is the closest relatives of multicellular animals, encodes early prototypes of p22phox, p47phox as well as the earliest known Nox2-like ancestor of the Nox1-3 subfamily. p67phox- and p47phox-like genes are seen in the sea urchin Strongylocentrotus purpuratus and the limpet Lottia gigantea that also possess Nox2-like co-orthologs of vertebrate Nox1-3. Duplication of primordial p47phox and p67phox genes occurred in vertebrates, with the duplicated branches evolving into NOXO1 and NOXA1. Analysis of characteristic domains of regulatory subunits suggests a novel view of the evolution of Nox: in fish, p40phox participated in regulating both Nox1 and Nox2, but after the appearance of mammals, Nox1 (but not Nox2) became independent of p40phox. In the fish Oryzias latipes, a NOXO1 ortholog retains an autoinhibitory region that is characteristic of mammalian p47phox, and this was subsequently lost from NOXO1 in later vertebrates. Detailed amino acid sequence comparisons identified both putative key residues conserved in characteristic domains and previously unidentified conserved regions. Also, candidate organizer/activator proteins in fungi and amoeba are identified and hypothetical activation models are suggested.

Conclusion

This is the first report to provide the comprehensive view of the molecular evolution of regulatory subunits for Nox enzymes. This approach provides clues for understanding the evolution of biochemical and physiological functions for regulatory-subunit-dependent Nox enzymes.

ROS, mitochondria and the regulation of autophagy

Accumulation of reactive oxygen species (ROS) is an oxidative stress to which cells respond by activating various defense mechanisms or, finally, by dying. At low levels, however, ROS act as signaling molecules in various intracellular processes. Autophagy, a process by which eukaryotic cells degrade and recycle macromolecules and organelles, has an important role in the cellular response to oxidative stress. Here, we review recent reports suggesting a regulatory role for ROS of mitochondrial origin as signaling molecules in autophagy, leading, under different circumstances, to either survival or cell death. We then discuss the relationship between mitochondria and autophagosomes and propose that mitochondria have an essential role in autophagosome biogenesis.

Accumulation of free adduct glycation, oxidation, and nitration products follows acute loss of renal function

Glycation, oxidation, and nitration of endogenous proteins occur spontaneously and these modifications are also present in foods. Increased levels of these chemical changes are associated with chronic renal failure; however, little is known about acute kidney failure. We measured these modifications of plasma protein and related free adducts in plasma following bilateral nephrectomy and bilateral ureteral obstruction. Advanced glycation end-product (AGE) residues of plasma protein were increased 3 h post-surgery, and thereafter slowly decreased in all groups, reflecting changes in plasma protein synthesis and transcapillary flow post-surgery. Ureteral ligation increased oxidation and nitration adduct residues. There were, however, marked increases in AGE, dityrosine, or 3-nitrotyrosine free adducts in both nephrectomized and ureter-ligated rats compared to rats that had undergone sham operations. There were lower modified adduct concentrations in the ureter-ligated compared to the nephrectomized rats, reflecting residual glomerular filtration and tubular removal. There was no increase in glycated, oxidized, and nitrated proteins. Glyoxal and methylglyoxal were also increased in both renal failure models. Our study shows that the acute loss of renal function and urinary excretion leads to the accumulation of AGE, oxidation, and nitration free adducts in the plasma.

Regulation of Nox and Duox enzymatic activity and expression

In recent years, it has become clear that reactive oxygen species (ROS, which include superoxide, hydrogen peroxide, and other metabolites) are produced in biological systems. Rather than being simply a by-product of aerobic metabolism, it is now recognized that specific enzymes--the Nox (NADPH oxidase) and Duox (Dual oxidase) enzymes--seem to have the sole function of generating ROS in a carefully regulated manner, and key roles in signal transduction, immune function, hormone biosynthesis, and other normal biological functions are being uncovered. The prototypical Nox is the respiratory burst oxidase or phagocyte oxidase, which generates large amounts of superoxide and other reactive species in the phagosomes of neutrophils and macrophages, playing a central role in innate immunity by killing microbes. This enzyme system has been extensively studied over the past two decades, and provides a basis for comparison with the more recently described Nox and Duox enzymes, which generate ROS in a variety of cells and tissues. This review first considers the structure and regulation of the respiratory burst oxidase, and then reviews recent studies relating to the regulation of the activity of the novel Nox/Duox enzymes. The regulation of Nox and Duox expression in tissues and by specific stimuli is also considered here. An accompanying review considers biological and pathological roles of the Nox family of enzymes.

Semagenesis and the parasitic angiosperm Striga asiatica

Over the last several years, intermediates in the reduction of dioxygen have been attributed diverse functional roles ranging from protection against pathogen attack to the regulation of cellular development. Evidence now suggests that parasitic angiosperms, which naturally commit to virulence through the growth of new organs, depend on reduced oxygen intermediates, or reactive oxygen species (ROS), for signal generation. Clearly, the role of ROS in both plant defense and other physiological responses complicates any models that employ these intermediates in host plant recognition. Here we exploit the transparent young Striga asiatica seedling to (i) localize the site of H(2)O(2) accumulation to the surface cells of the primary root meristem, (ii) demonstrate the accumulation of H(2)O(2) within cytoplasmic and apoplastic compartments, and (iii) document precise regulation of H(2)O(2) accumulation during development of the host attachment organ, the haustorium. These studies reveal a new active process for signal generation, host detection and commitment that is capable of ensuring the correct spatial and temporal positioning for attachment.

Nox enzymes, ROS, and chronic disease: an example of antagonistic pleiotropy

Reactive oxygen species (ROS) are considered to be chemically reactive with and damaging to biomolecules including DNA, protein, and lipid, and excessive exposure to ROS induces oxidative stress and causes genetic mutations. However, the recently described family of Nox and Duox enzymes generates ROS in a variety of tissues as part of normal physiological functions, which include innate immunity, signal transduction, and biochemical reactions, e.g., to produce thyroid hormone. Nature's "choice" of ROS to carry out these biological functions seems odd indeed, given its predisposition to cause molecular damage. This review describes normal biological roles of Nox enzymes as well as pathological conditions that are associated with ROS production by Nox enzymes. By far the most common conditions associated with Nox-derived ROS are chronic diseases that tend to appear late in life, including atherosclerosis, hypertension, diabetic nephropathy, lung fibrosis, cancer, Alzheimer's disease, and others. In almost all cases, with the exception of a few rare inherited conditions (e.g., related to innate immunity, gravity perception, and hypothyroidism), diseases are associated with overproduction of ROS by Nox enzymes; this results in oxidative stress that damages tissues over time. I propose that these pathological roles of Nox enzymes can be understood in terms of antagonistic pleiotropy: genes that confer a reproductive advantage early in life can have harmful effects late in life. Such genes are retained during evolution despite their harmful effects, because the force of natural selection declines with advanced age. This review discusses some of the proposed physiologic roles of Nox enzymes, and emphasizes the role of Nox enzymes in disease and the likely beneficial effects of drugs that target Nox enzymes, particularly in chronic diseases associated with an aging population.

Generation of reactive oxygen species by fungal NADPH oxidases is required for rice blast disease

One of the first responses of plants to microbial attack is the production of extracellular superoxide surrounding infection sites. Here, we report that Magnaporthe grisea, the causal agent of rice blast disease, undergoes an oxidative burst of its own during plant infection, which is associated with its development of specialized infection structures called appressoria. Scavenging of these oxygen radicals significantly delayed the development of appressoria and altered their morphology. We targeted two superoxide-generating NADPH oxidase-encoding genes, Nox1 and Nox2, and demonstrated genetically, that each is independently required for pathogenicity of M. grisea. Deltanox1 and Deltanox2 mutants are incapable of causing plant disease because of an inability to bring about appressorium-mediated cuticle penetration. The initiation of rice blast disease therefore requires production of superoxide by the invading pathogen.

Molecular evolution of the reactive oxygen-generating NADPH oxidase (Nox/Duox) family of enzymes

Background

NADPH-oxidases (Nox) and the related Dual oxidases (Duox) play varied biological and pathological roles via regulated generation of reactive oxygen species (ROS). Members of the Nox/Duox family have been identified in a wide variety of organisms, including mammals, nematodes, fruit fly, green plants, fungi, and slime molds; however, little is known about the molecular evolutionary history of these enzymes.

Results

We assembled and analyzed the deduced amino acid sequences of 101 Nox/Duox orthologs from 25 species, including vertebrates, urochordates, echinoderms, insects, nematodes, fungi, slime mold amoeba, alga and plants. In contrast to ROS defense enzymes, such as superoxide dismutase and catalase that are present in prokaryotes, ROS-generating Nox/Duox orthologs only appeared later in evolution. Molecular taxonomy revealed seven distinct subfamilies of Noxes and Duoxes. The calcium-regulated orthologs representing 4 subfamilies diverged early and are the most widely distributed in biology. Subunit-regulated Noxes represent a second major subdivision, and appeared first in fungi and amoeba. Nox5 was lost in rodents, and Nox3, which functions in the inner ear in gravity perception, emerged the most recently, corresponding to full-time adaptation of vertebrates to land. The sea urchin Strongylocentrotus purpuratus possesses the earliest Nox2 co-ortholog of vertebrate Nox1, 2, and 3, while Nox4 first appeared somewhat later in urochordates. Comparison of evolutionary substitution rates demonstrates that Nox2, the regulatory subunits p47phox and p67phox, and Duox are more stringently conserved in vertebrates than other Noxes and Nox regulatory subunits. Amino acid sequence comparisons identified key catalytic or regulatory regions, as 68 residues were highly conserved among all Nox/Duox orthologs, and 14 of these were identical with those mutated in Nox2 in variants of X-linked chronic granulomatous disease. In addition to canonical motifs, the B-loop, TM6-FAD, VXGPFG-motif, and extreme C-terminal regions were identified as important for Nox activity, as verified by mutational analysis. The presence of these non-canonical, but highly conserved regions suggests that all Nox/Duox may possess a common biological function remained in a long history of Nox/Duox evolution.

Conclusion

This report provides the first comprehensive analysis of the evolution and conserved functions of Nox and Duox family members, including identification of conserved amino acid residues. These results provide a guide for future structure-function studies and for understanding the evolution of biological functions of these enzymes.

Nox regulation of smooth muscle contraction

The catalytic subunit gp91phox (Nox2) of the NADPH oxidase of mammalian phagocytes is activated by microbes and immune mediators to produce large amounts of reactive oxygen species (ROS) which participate in microbial killing. Homologs of gp91phox, the Nox and Duox enzymes, were recently described in a range of organisms, including plants, vertebrates, and invertebrates such as Drosophila melanogaster. While their enzymology and cell biology are being extensively studied in many laboratories, little is known about in vivo functions of Noxes. Here, we establish and use an inducible system for RNAi to discover functions of dNox, an ortholog of human Nox5 in Drosophila. We report here that depletion of dNox in musculature causes retention of mature eggs within ovaries, leading to female sterility. In dNox-depleted ovaries and ovaries treated with a Nox inhibitor, muscular contractions induced by the neuropeptide proctolin are markedly inhibited. This functional defect results from a requirement for dNox-for the proctolin-induced calcium flux in Drosophila ovaries. Thus, these studies demonstrate a novel biological role for Nox-generated ROS in mediating agonist-induced calcium flux and smooth muscle contraction.

Depolarization of the macula densa induces superoxide production via NAD(P)H oxidase

Superoxide (O2−) enhances tubuloglomerular feedback by scavenging nitric oxide at the macula densa. However, the singling pathway of O2−production in the macula densa is not known. We hypothesized that the increase in tubular NaCl concentration that initiates tubuloglomerular feedback induces O2−production by the macula densa via NAD(P)H oxidase, which is activated by macula densa depolarization. We isolated and microperfused the thick ascending limb of the loop of Henle and attached macula densa in rabbits. A fluorescent dye, dihydroethidium, was used to detect O2−production at the macula densa. When luminal NaCl was switched from 10 to 80 mM, a situation of initiating maximum tubuloglomerular feedback response, O2−production significantly increased. To make sure that the shifts in the oxyethidium/dihydroethidium ratio were due to changes in O2−, we used tempol (10−4M), a stable membrane-permeant superoxide dismutase mimetic. With tempol present, when we switched from 10 to 80 mM NaCl, the increase in oxyethidium/dihydroethidium ratio was blocked. To determine the source of O2−, we used the NAD(P)H oxidase inhibitor apocynin. When luminal NaCl was switched from 10 to 80 mM in the presence of apocynin, O2−production was inhibited by 80%. To see whether the effect of increasing luminal NaCl involves Na-K-2Cl cotransporters, we inhibited them with furosemide. When luminal NaCl was switched from 10 to 80 mM in the presence of furosemide, O2−production was blocked. To test whether depolarization of the macula densa induces O2−production, we artificially induced depolarization by adding valinomycin (10−6M) and 25 mM KCl to the luminal perfusate. Depolarization alone significantly increases O2−production. We conclude that increasing luminal NaCl induces O2−production during tubuloglomerular feedback. O2−generated by the macula densa is primarily derived from NAD(P)H oxidase and is induced by depolarization.

Oxidative stress enzymes are required for DAF-16-mediated immunity due to generation of reactive oxygen species by Caenorhabditis elegans

Caenorhabditis elegans has recently been developed as a model for microbial pathogenesis, yet little is known about its immunological defenses. Previous work implicated insulin signaling in mediating pathogen resistance in a manner dependent on the transcriptional regulator DAF-16, but the mechanism has not been elucidated. We present evidence that C. elegans, like mammalian phagocytes, produces reactive oxygen species (ROS) in response to pathogens. Signs of oxidative stress occur in the intestine - the site of the host-pathogen interface - suggesting that ROS release is localized to this tissue. Evidence includes the accumulation of lipofuscin, a pigment resulting from oxidative damage, at this site. In addition, SOD-3, a superoxide dismutase regulated by DAF-16, is induced in intestinal tissue after exposure to pathogenic bacteria. Moreover, we show that the oxidative stress response genes sod-3 and ctl-2 are required for DAF-16-mediated resistance to Enterococcus faecalis using a C. elegans killing assay. We propose a model whereby C. elegans responds to pathogens by producing ROS in the intestine while simultaneously inducing a DAF-16-dependent oxidative stress response to protect adjacent tissues. Because insulin-signaling mutants overproduce oxidative stress response enzymes, the model provides an explanation for their increased resistance to pathogens.

Developmental regulation of DUOX1 expression and function in human fetal lung epithelial cells

The purpose of this study was to determine the expression and cellular functions of the epithelial NADPH oxidase DUOX1 during alveolar type II cell development. When human fetal lung cells (gestational age 11-22 wk) were cultured to confluency on permeable filters, exposure of cells to a hormone mixture (dexamethasone, 8-Br-cAMP, and IBMX, together referred to as DCI) resulted in differentiation of cells into a mature type II phenotype as assessed by expression of lamellar bodies, surfactant proteins, and transepithelial electrical parameters. After 6 days in culture in presence of DCI, transepithelial resistance (2,616 +/- 529 Omega.cm(2)) and potential (-8.5 +/- 0.6 mV) indicated epithelial polarization. At the same time, treatment with DCI significantly increased the mRNA expression of DUOX1 ( approximately 21-fold), its maturation factor DUOXA1 ( approximately 12-fold), as well as DUOX protein ( approximately 12-fold), which was localized near the apical cell pole in confluent cultures. For comparison, in fetal lung specimens, DUOX protein was not detectable at up to 27 wk of gestational age but was strongly upregulated after 32 wk. Function of DUOX1 was assessed by measuring H(2)O(2) and acid production. Rates of H(2)O(2) production were increased by DCI treatment and blocked by small interfering RNA directed against DUOX1 or by diphenylene iodonium. DCI-treated cultures also showed increased intracellular acid production and acid release into the mucosal medium, and acid production was largely blocked by knockdown of DUOX1 mRNA. These data establish the regulated expression of DUOX1 during alveolar maturation, and indicate DUOX1 in alveolar H(2)O(2) and acid secretion by differentiated type II cells.

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

CD95 activation in the liver: ion fluxes and oxidative signaling

Apoptosis is characterized by typical features as cell shrinkage, nuclear condensation, DNA fragmentation, and apoptotic body formation. Whereas some signs of apoptosis are cell type-and death signal-dependent, apoptotic cell volume decrease is an early and ubiquitous event and little is known about the signalling events, which are localized upstream of the plasma membrane transport steps leading to apoptotic cell volume decrease and the proapoptotic events, which are induced by osmolyte loss and cell shrinkage. Ion fluxes and oxidative signaling were recently shown to play an important role in signal transduction with respect to apoptotic cell death within the liver, as a ceramide-dependent activation of the NADPH oxidase was identified as the source of reactive oxygen species generation in rat hepatocytes upon treatment with CD95 ligand, hydrophobic bile salts or hyperosmolarity. The NADPH oxidase-derived ROS signal then allows via Yes, JNK, and EGFR activation for CD95 tyrosine phosphorylation as a prerequisite for CD95 targeting to the plasma membrane and formation of the death inducing signalling complex. Other covalent modifications such as CD95-tyrosine-nitration or CD95-serine/threonine-phosphorylation can interfere with the CD95 activation process. The findings not only provide a mechanistic explanation for the high susceptibility of dehydrated cells for apoptosis, but also give insight into the role of ion fluxes and oxidative signaling with respect to apoptotic cell death within the liver.

Biomphalaria glabrata transcriptome: identification of cell-signalling, transcriptional control and immune-related genes from open reading frame expressed sequence tags (ORESTES)

Biomphalaria glabrata is the major intermediate snail host for Schistosoma mansoni, one of the important schistosomes infecting man. Much remains to be discovered concerning specific molecules mediating the defence events in these intermediate hosts, triggered by invading schistosomes. An expressed sequence tag (EST) gene discovery strategy known as ORESTES has been employed to identify transcripts that might be involved in snail-schistosome interactions in order to examine gene expression patterns in infected B. glabrata. Over 3930 ESTs were sequenced from cDNA libraries made from both schistosome-exposed and unexposed snails using different tissue types, producing a database of 1843 non-redundant clones. The non-redundant set has been assessed for gene ontology and KEGG pathway assignments. This approach has revealed a number of signalling, antioxidant and immune-related gene homologues that, based on current understanding of molluscan and other comparative systems, might play an important role in the molluscan defence response towards infection.

Hyperosmotic Activation of the CD95 System

Cell shrinkage, nuclear condensation, DNA fragmentation, and apoptotic body formation are hallmarks of programmed apoptotic cell death. Herein, apoptotic volume decrease (AVD) is an early and ubiquitous event. Conversely, in hepatocytes, hyperosmotic cell shrinkage leads to an activation of the CD95 death receptor system, which involves CD95 tyrosine phosphorylation, CD95 oligomerization, and subsequent trafficking of the CD95 to the plasma membrane, and sensitizes hepatocytes toward CD95 ligand (CD95L)-induced apoptosis. Early signaling events leading to CD95 activation by hyperosmolarity have been identified. In hepatocytes, hyperosmotic exposure induces an almost instantaneous acidification of an acidic sphingomyelinase (ASM) containing endosomal compartment, which is followed by an increase in the intracellular ceramide concentration. Inhibition of anion channels or the vacuolar-type H(+)-ATPase abolishes not only endosomal acidification and subsequent ceramide generation, but also the otherwise observed hyperosmotically induced generation of reactive oxygen species (ROS) by NADPH oxidase isoforms. Hyperosmolarity-induced ROS formation then leads to a Src-family kinase Yes-mediated activation of the epidermal growth factor receptor (EGFR) and to an activation of the c-Jun-N-terminal kinase (JNK). JNK then provides a signal for CD95/EGFR association and subsequent CD95 tyrosine phosphorylation, which is mediated by the EGFR tyrosine kinase activity. CD95 tyrosine phosphorylation then allows for CD95 receptor oligomerization, translocation of the CD95/EGFR protein complex to the plasma membrane, and formation of the death inducing signaling complex (DISC). Mild hyperosmotic exposure, that is, 405 mosmol/liter, does not lead to a reduction of cell viability, even if DISC formation and subsequent caspase 8 and 3 activation occur, but sensitizes hepatocytes to CD95L-induced apoptosis. However, activation of the CD95 system by a more severe hyperosmotic challenge (>505 mosmol/liter) is followed by execution of the apoptotic cell death. Other covalent modifications of CD95, such as CD95 tyrosine nitration or CD95 serine/threonine phosphorylation, were shown to inhibit the CD95 activation process.

Duox2 exhibits potent heme peroxidase activity in human respiratory tract epithelium

The dual oxidase isozymes Duox1 and Duox2 exhibit functional NADPH:O(2) oxidoreductase activity in thyroid and respiratory tract cells and are thought to be essential for H(2)O(2) generation in these tissues. However, it is not universally accepted that the heme peroxidase domains of the Duox isozymes are functional. To address this question, we modulated Duox2 expression in human tracheobronchial epithelial (TBE) cell culture systems and quantified peroxidase activity. We discovered that interferon-gamma (IFN-gamma) induced robust peroxidase activity in TBE cells that paralleled Duox2 expression. IFN-gamma-induced peroxidase activity was abolished in the presence of sodium azide, which implicated the activation of a heme peroxidase. IFN-gamma-induced peroxidase activity was abolished in TBE cell lines expressing anti-Duox2 short hairpin RNA transcripts. Together, these data unequivocally demonstrated that Duox2 contains a functional heme peroxidase in intact respiratory tract epithelium.

Role of Nox family NADPH oxidases in host defense

The phagocytic NADPH oxidase is recognized as a critical component of innate immunity, responsible for generation of microbicidal reactive oxygen species (ROS). This enzyme is one representative of the Nox family of oxidases (Nox1-Nox5, Duox1, and Duox2) that exhibit diverse expression patterns and appear to serve a variety of functions related to ROS generation. Mounting evidence now suggests that several of these novel oxidases also serve in host defense, particularly those showing high expression along epithelial surfaces exposed to the external environment. Within these sites, Nox enzymes tend to be located on apical cell surfaces and release ROS into extracellular environments, where they can be used by known antimicrobial peroxidases. Moreover, microbial factors were shown in several cases to cause higher ROS production, either by direct oxidase activation or by inducing higher oxidase expression. Several oxidases are also induced by immune cytokines, including interferon-gamma, interleukin (IL)-4, and IL-13. Although most of the evidence supporting host defense roles for mammalian nonphagocytic oxidases remains circumstantial, recent evidence indicates that Drosophila Duox plays a role in host resistance to infection. Finally, oxidative defense against invading pathogens appears to be an ancient protective mechanism, because related oxidases are known to participate in disease resistance in plants.

Physiology and pathophysiology of the DUOXes

The dual oxidases (DUOXes) 1 and 2 are named based on their having both a domain homologous to the NADPH-oxidase of the phagocyte NADPH-oxidase gp91( phox )/NOX2 and a domain homologous to thyroid peroxidase. The DUOX1 and DUOX2 mRNAs were originally cloned from thyroid tissue, and the corresponding proteins were recognized as intricate components of the thyroid hormone synthesis process, providing hydrogen peroxide essential for the organification of iodide. The function of DUOX2 in thyroid hormonogenesis has been firmly established by linking the congenital hypothyroid phenotype "total iodide organification defect" to biallelic inactivating DUOX2 mutations. Based on the expression of both DUOXes in combination with a peroxidase in a range of different tissues and functional studies; the concept evolves that DUOX is important not only for thyroid hormonogenesis but also as an integral part of the host defense system of mucosal surfaces, participates in the control of epithelial infection, augments surface B-cell receptor signaling in lymphocytes, and is involved in generating a respiratory burst at fertilization.

Endosomal Acidification and Activation of NADPH Oxidase Isoforms Are Upstream Events in Hyperosmolarity-induced Hepatocyte Apoptosis

Hyperosmotic exposure of rat hepatocytes induced a rapid oxidative-stress(ROS) response as an upstream signal for proapoptotic CD95 activation. This study shows that hyperosmotic ROS formation involves a rapid ceramide- and protein kinase Czeta (PKCzeta)-dependent serine phosphorylation of p47phox and subsequent activation of NADPH oxidase isoforms. Hyperosmotic p47phox phosphorylation and ROS formation were sensitive to inhibition of sphingomyelinases and were strongly blunted after knockdown of acidic sphingomyelinase (ASM) or of p47phox protein. Hyperosmolarity induced a rapid bafilomycin- and 4,4 '-diisothiocyanostilbene-2,2 '-disulfonic acid disodium salt (DIDS)-sensitive acidification of a vesicular compartment, which was accessible to endocytosed fluorescein isothiocyanate-dextran and colocalized with ASM, PKCzeta, and the NADPH oxidase isoform Nox 2 (gp91phox). Bafilomycin and DIDS prevented the hyperosmolarity-induced increase in ceramide formation, p47phox phosphorylation, and ROS formation. As shown recently (Reinehr, R., Becker, S., Höngen, A., and Häussinger, D. (2004) J. Biol. Chem. 279, 23977-23987), hyperosmolarity induced a Yes-dependent activation of JNK and the epidermal growth factor receptor (EGFR), followed by EGFR-CD95 association, EGFR-catalyzed CD95-tyrosine phosphorylation, and translocation of the EGFR-CD95 complex to the plasma membrane, where formation of the deathinducing signaling complex occurs. These proapoptotic responses were not only sensitive to inhibitors of sphingomyelinase, PKCzeta, or NADPH oxidases but also to ASM knockdown, bafilomycin, and DIDS, i.e. maneuvers largely preventing hyperosmolarity-induced endosomal acidification and/or ceramide formation. In hepatocytes from p47phox knock-out mice, hyperosmolarity failed to activate the CD95 system. The data suggest that hyperosmolarity induces endosomal acidification as an important upstream event for CD95 activation through stimulation of ASM-dependent ceramide formation and activation of NADPH oxidase isoforms.

Restricted expression of NADPH oxidase/peroxidase gene (Duox) in zone VII of the ascidian endostyle

The ascidian Ciona intestinalis, a marine invertebrate chordate, is an emerging model system for developmental and evolutionary studies. The endostyle, one of the characteristic organs of ascidians, is a pharyngeal structure with iodine-concentrating and peroxidase activities and is therefore considered to be homologous to the follicular thyroid of higher vertebrates. We have previously reported that a limited part of the endostyle (zone VII) is marked by the expression of orthologs of the thyroid peroxidase (TPO) and thyroid transcription factor-2 (TTF-2/FoxE) genes. In this study, we have identified the Ciona homolog of NADPH oxidase/peroxidase (Duox), which provides hydrogen peroxide (H(2)O(2)) for iodine metabolism by TPO in the vertebrate thyroid. Expression patterns assessed by in situ hybridization have revealed that Ciona Duox (Ci-Duox) is predominantly expressed in the dorsal part of zone VII of the endostyle. Furthermore, two-color fluorescent in situ hybridization with Ci-Duox and Ciona TPO (CiTPO) has revealed that the ventral boundary of the Ci-Duox domain of expression is more dorsal than that of CiTPO. We have also characterized several genes, such as Ci-Fgf8/17/18, 5HT7, and Ci-NK4, which are predominantly expressed in the ventral part of zone VII, in a region complementary to the Ci-Duox expression domain. These observations suggest that, at the molecular level, zone VII has a complex organization that might have some impact on the specification of cell types and functions in this thyroid-equivalent element of the ascidian endostyle.

Dual oxidases

Reactive oxygen species (ROS) have an important role in various physiological processes including host defence, mitogenesis, hormone biosynthesis, apoptosis and fertilization. Currently, the most characterized ROS-producing system operates in phagocytic cells, where ROS generated during phagocytosis act in host defence. Recently, several novel homologues of the phagocytic oxidase have been discovered and this protein family is now designated as the NOX/DUOX family of NADPH oxidases. NOX/DUOX enzymes function in a variety of tissues, including colon, kidney, thyroid gland, testis, salivary glands, airways and lymphoid organs. Importantly, members of the enzyme family are also found in non-mammalian species, including Caenorhabditis elegans and sea urchin. The physiological functions of novel NADPH oxidase enzymes are currently largely unknown. This review focuses on our current knowledge about dual oxidases.

[Anti-neutrophil cytoplasmic antibody MPO-ANCA related with disease activity of vasculitis]

Myeloperoxidase (MPO)-specific anti-neutrophil cytoplasmic antibodies (MPO-ANCA) are involved in the development of vasculitis microscopic polyangiitis, a systemic vasculitis etc. We have showed a correlation of MPO-ANCA epitopes in vasculitis concerning contribution of N and C terminus of MPO to severity of the diseases. On the other hand, a role of activated neutrophils in inflammatory nephritis renal lesions using SCG/Kj mice. In the phase of nephritis with a low grade of proteinuria, the spontaneous release of MPO from peripheral neutrophils increased, indicating that neutrophils are activated and contribute to the development of active crescentic lesions in SCG/Kj mice. In addition, we have investigated that mice having CADS/CAWS-induced vasculitis also are good model animals for the analysis of the production of MPO-ANCA. Furthermore, we have clarified that MPO is a major antigen for MPO-ANCA production using MPO knock mice.

Hyperosmotic activation of the CD95 death receptor system

Apoptosis is characterized by cell shrinkage, nuclear condensation, DNA fragmentation and apoptotic body formation. These features distinguish apoptosis from other types of cell death, such as necrosis. Whereas some signs of apoptosis, such as externalization of phosphatidylserine, altered mitochondrial function or activation of caspases are cell type- and death signal-dependent, apoptotic cell volume decrease (AVD) is an early and ubiquitous event and little is known about the signalling events, which are localized upstream of the plasma membrane transport steps leading to AVD and the proapoptotic events, which are induced by osmolyte loss and cell shrinkage. In hepatocytes hyperosmotic shrinkage sensitizes the cells towards CD95 ligand-induced apoptosis by activating the CD95 system. This complex process with a NADPH oxidase-derived reactive oxygen species signal as an important upstream event, allows via Yes, JNK and epidermal growth factor-receptor activation for CD95 tyrosine phosphorylation as a prerequisite for CD95 targeting to the plasma membrane and formation of the death inducing signalling complex. Other covalent modifications such as CD95-tyrosine-nitration or CD95-serine/threonine-phosphorylation can interfere with the CD95 activation process. The findings not only provide a mechanistic explanation for the high susceptibility of dehydrated cells for apoptosis, but also give insight into the role of AVD.

Is vitamin E a safe prophylaxis for preeclampsia?

The prophylactic use of vitamins E and C for the prevention of preeclampsia is currently being evaluated in multiple clinical trials in Canada, Mexico, the United Kingdom, the United States, and other developing countries. In addition to its antioxidant capacity, exogenous vitamin E may prevent an immunologic switch (Th1 to Th2) that is vital for early-to late transition in normal pregnancies. Moreover, vitamin E could be a potential interferon-gamma (IFN-gamma) mimic facilitating persistent proinflammatory reactions at the fetal-maternal interface. These untoward effects of dietary intake of vitamin E may be more pronounced in those treated cases that fail to develop preeclampsia. A critical test of this hypothesis would be to establish whether, under variable O2 tension, vitamin E is capable of affecting cytokine signaling in placental trophoblasts and maternal immune effector cells, both in early and late human pregnancies.

NADPH oxidases in cardiovascular health and disease

Increased oxidative stress plays an important role in the pathophysiology of cardiovascular diseases such as hypertension, atherosclerosis, diabetes, cardiac hypertrophy, heart failure, and ischemia-reperfusion. Although several sources of reactive oxygen species (ROS) may be involved, a family of NADPH oxidases appears to be especially important for redox signaling and may be amenable to specific therapeutic targeting. These include the prototypic Nox2 isoform-based NADPH oxidase, which was first characterized in neutrophils, as well as other NADPH oxidases such as Nox1 and Nox4. These Nox isoforms are expressed in a cell- and tissue-specific fashion, are subject to independent activation and regulation, and may subserve distinct functions. This article reviews the potential roles of NADPH oxidases in both cardiovascular physiological processes (such as the regulation of vascular tone and oxygen sensing) and pathophysiological processes such as endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, angiogenesis, and vascular and cardiac remodeling. The complexity of regulation of NADPH oxidases in these conditions may provide the possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the disease process.