Function of reactive oxygen species during animal development: Passive or active?

Vertebrate-specific glutaredoxin is essential for brain development

Cellular functions and survival are dependent on a tightly controlled redox potential. Currently, an increasing amount of data supports the concept of local changes in the redox environment and specific redox signaling events controlling cell function. Specific protein thiol groups are the major targets of redox signaling and regulation. Thioredoxins and glutaredoxins catalyze reversible thiol-disulfide exchange reactions and are primary regulators of the protein thiol redox state. Here, we demonstrate that embryonic brain development depends on the enzymatic activity of glutaredoxin 2. Zebrafish with silenced expression of glutaredoxin 2 lost virtually all types of neurons by apoptotic cell death and the ability to develop an axonal scaffold. As demonstrated in zebrafish and in a human cellular model for neuronal differentiation, glutaredoxin 2 controls axonal outgrowth via thiol redox regulation of collapsin response mediator protein 2, a central component of the semaphorin pathway. This study provides an example of a specific thiol redox regulation essential for vertebrate embryonic development.

Roles of reactive oxygen species in female reproduction

Reactive oxygen species (ROS) are highly reactive oxidizing agents. Cells, under aerobic conditions, have a defence system against ROS, and in normal circumstances, there is an appropriate balance between pro-oxidants and antioxidants. When an overproduction of ROS develops or the body fails to eliminate ROS in excess, oxidative stress arises, during which ROS accumulate and damage cells and tissues. Besides their noxious effects, accumulating data have shown that controlled and adequate ROS concentrations exert physiologic functions. Different studies have confirmed the presence of ROS and the transcripts of the various antioxidant enzymes in the female reproductive tract. When ROS production overwhelms antioxidant defences, oxidative stress occurs, which may deeply threaten the anatomical and functional integrity of the genital tract. This review addresses the main physiological and pathological roles exerted by ROS and their scavenging systems in several processes involved in the main physiological functions of the female reproductive tract of both women and domestic animals. Particularly, the involvement of the oxidant system in several reproductive processes is investigated, such as follicular development, ovarian steroidogenesis, ovulation, corpus luteum formation and function, luteolysis, germ cell function, maintenance of pregnancy and beginning of parturition.

The Roles of Glutathione Peroxidases during Embryo Development

Embryo development relies on the complex interplay of the basic cellular processes including proliferation, differentiation, and apoptotic cell death. Precise regulation of these events is the basis for the establishment of embryonic structures and the organ development. Beginning with fertilization of the oocyte until delivery the developing embryo encounters changing environmental conditions such as varying levels of oxygen, which can give rise to reactive oxygen species (ROS). These challenges are met by the embryo with metabolic adaptations and by an array of anti-oxidative mechanisms. ROS can be deleterious by modifying biological molecules including lipids, proteins, and nucleic acids and may induce abnormal development or even embryonic lethality. On the other hand ROS are vital players of various signaling cascades that affect the balance between cell growth, differentiation, and death. An imbalance or dysregulation of these biological processes may generate cells with abnormal growth and is therefore potentially teratogenic and tumorigenic. Thus, a precise balance between processes generating ROS and those decomposing ROS is critical for normal embryo development. One tier of the cellular protective system against ROS constitutes the family of selenium-dependent glutathione peroxidases (GPx). These enzymes reduce hydroperoxides to the corresponding alcohols at the expense of reduced glutathione. Of special interest within this protein family is the moonlighting enzyme glutathione peroxidase 4 (Gpx4). This enzyme is a scavenger of lipophilic hydroperoxides on one hand, but on the other hand can be transformed into an enzymatically inactive cellular structural component. GPx4 deficiency - in contrast to all other GPx family members - leads to abnormal embryo development and finally produces a lethal phenotype in mice. This review is aimed at summarizing the current knowledge on GPx isoforms during embryo development and tumor development with an emphasis on GPx4.

A mammalian monothiol glutaredoxin, Grx3, is critical for cell cycle progression during embryogenesis

Glutaredoxins (Grxs) have been shown to be critical in maintaining redox homeostasis in living cells. Recently, an emerging subgroup of Grxs with one cysteine residue in the putative active motif (monothiol Grxs) has been identified. However, the biological and physiological functions of this group of proteins have not been well characterized. Here, we characterize a mammalian monothiol Grx (Grx3, also termed TXNL2/PICOT) with high similarity to yeast ScGrx3/ScGrx4. In yeast expression assays, mammalian Grx3s were localized to the nuclei and able to rescue growth defects of grx3grx4 cells. Furthermore, Grx3 inhibited iron accumulation in yeast grx3gxr4 cells and suppressed the sensitivity of mutant cells to exogenous oxidants. In mice, Grx3 mRNA was ubiquitously expressed in developing embryos, adult tissues and organs, and was induced during oxidative stress. Mouse embryos absent of Grx3 grew smaller with morphological defects and eventually died at 12.5 days of gestation. Analysis in mouse embryonic fibroblasts revealed that Grx3(-/-) cells had impaired growth and cell cycle progression at the G(2) /M phase, whereas the DNA replication during the S phase was not affected by Grx3 deletion. Furthermore, Grx3-knockdown HeLa cells displayed a significant delay in mitotic exit and had a higher percentage of binucleated cells. Therefore, our findings suggest that the mammalian Grx3 has conserved functions in protecting cells against oxidative stress and deletion of Grx3 in mice causes early embryonic lethality which could be due to defective cell cycle progression during late mitosis.

Stimulation of cardiomyogenesis of embryonic stem cells by nitric oxide downstream of AMP-activated protein kinase and mTOR signaling pathways

Nitric oxide (NO) is a key regulator of cardiomyogenesis of embryonic stem (ES) cells. However, signaling pathways involving the energy sensor AMP-activated protein kinase (AMPK) and/or mammalian target of rapamycin (mTOR) resulting in NO generation and stimulation of cardiomyogenesis are currently not known. Herein, the role of AMPK- versus mTOR-regulated signaling pathways and the impact of NO for cardiomyogenesis of mouse ES cells were investigated. Activation of AMPK by 5-amino-4-imidazolecarboxamide riboside (AICAr) or metformin as well as inactivation of AMPK by compound C (Comp C), siRNA ablation of AMPKα2, or exogenous ATP stimulated cardiomyogenesis of ES cells. Inhibition of AMPK by Comp C resulted in phosphorylation of mTOR and generation of NO. NO generation was likewise achieved when AMPK was either activated by AICAr or mTOR was inhibited by rapamycin, suggesting that NO generation occurred by two mutually active parallel signaling pathways, one being AMPK dependent and mTOR independent (AICAr pathway) and the other being AMPK independent and mTOR dependent (Comp C pathway). Consequently, cardiomyogenesis as well as NO generation was completely abrogated when ES cells were cultivated in the presence of rapamycin and Comp C, which inhibit both signaling pathways. The impact of NO for cardiomyogenesis of ES cells was corroborated in experiments showing that the effects of Comp C on cardiomyogenesis of ES cells were abolished by the NO synthase inhibitors NG-monomethyl-l-arginine and N (G)-nitro-l-arginine methyl ester. In summary, our data demonstrate that NO generation downstream of AMPK and mTOR is activated by distinct, interacting signaling pathways that initiate cardiomyogenesis of ES cells.

Male gender significantly increases risk of oxidative stress related congenital anomalies in the non-diabetic population

OBJECTIVE

Oxidative stress (OS) is an important mechanism of teratogenesis. Recent work suggests increased OS in males. We evaluated whether male gender increased the risk of cyanotic congenital heart defects (CCHD) whose development is linked to OS and other common congenital anomalies (CA) in non-diabetic pregnancies.

METHODS

CDC-National Center for Health Statistics data for 19 states in 2006 were reviewed. CCHD, anencephaly, spina bifida, congenial diaphragmatic hernia (CDH), omphalocele, gastroschisis, limb defects, cleft lip with or without cleft palate (CL/P) and isolated cleft palate were evaluated. Adjusted odds ratio (OR) (95% CI) were calculated for CA in males with females as the reference group.

RESULTS

Of 1,194, 581, cases analyzed after exclusions, 3037 (0.25%) had major CA. Males had elevated adjusted OR (95% CI) for CCHD: 1.198 (1.027, 1.397), CDH: 1.487 (1.078, 2.051), and CL/P: 1.431 (1.24, 1.651). There was a significant interaction between cigarette use and (male) fetal gender and also with maternal age in the CL/P group.

CONCLUSIONS

In non-diabetic pregnancies, male gender appears to be an independent risk factor for some types of CA believed to be associated with OS. Cigarette smoking, a well recognized source of OS only increased the risk of CL/P in males.

Physiological effects of Type 2 diabetes on mRNA processing and gene expression

Characteristics of Type 2 diabetes include both high blood glucose (hyperglycemia) and raised cholesterol and triglycerides (hyperlipidemia). Several studies have now shown that both hyperglycemia and hyperlipidemia can alter gene expression by disrupting physiological mechanisms of gene regulation, including alternative mRNA splicing, epigenetic gene regulation and miRNA-mediated regulation of gene expression. These processes may also be influenced by intracellular oxidative stress, which is increased in diabetes and in response to hyperglycemia and hyperlipidemia. Many pathways relevant to diabetes are affected by altered gene expression, including lipid and glucose metabolism and oxidative phosphorylation. This article considers how hyperglycemia and hyperlipidemia can alter gene expression in diabetes, which could potentially contribute to the worsening of the diabetic phenotype and diabetic complications.

SIRT1 deficiency downregulates PTEN/JNK/FOXO1 pathway to block reactive oxygen species-induced apoptosis in mouse embryonic stem cells

Silent mating type information regulation 2 homolog 1 (SIRT1) plays a critical role in reactive oxygen species-triggered apoptosis in mouse embryonic stem (mES) cells. Here, we investigated a possible role for the PTEN/Akt/JNK pathway in the SIRT1-mediated apoptosis pathway in mES cells. Akt was activated by removal of anti-oxidant 2-mercaptoethanol in SIRT1(-/-) mES cells. Since PTEN is a negative regulator of Akt and its activity can be modulated by acetylation, we investigated if SIRT1 deacetylated PTEN to downregulate Akt to trigger apoptosis in anti-oxidant-free culture conditions. PTEN was hyperacetylated and excluded from the nucleus in SIRT1(-/-) mES cells, consistent with enhanced Akt activity. SIRT1 deficiency enhanced the acetylation/phosphorylation level of FOXO1 and subsequently inhibited the nuclear localization of FOXO1. Cellular acetylation levels were enhanced by DNA-damaging agent, not by removal of anti-oxidant. c-Jun NH2-terminal kinase (JNK) was activated by removal of anti-oxidant in SIRT1-dependent manner. Although p53 acetylation was stronger in SIRT1(-/-) mES cells, DNA-damaging stress activated phosphorylation and enhanced cellular levels of p53 irrespective of SIRT1, whereas removal of anti-oxidant slightly activated p53 only with SIRT1. Expression levels of Bim and Puma were increased in anti-oxidant-free culture conditions in an SIRT1-dependent manner and treatment with JNK inhibitor blocked induction of Bim expression. DNA-damaging agent activated caspase3 regardless of SIRT1. Our data support an important role for SIRT1 in preparing the PTEN/JNK/FOXO1 pathway to respond to cellular reactive oxygen species.

Teratogenicity and embryotoxicity in aquatic organisms after pesticide exposure and the role of oxidative stress

Many pesticides have been documented to induce embryotoxicity and teratogenicity in non-target aquatic biota such a fish, amphibians and invertebrates. Our review of the existing literature shows that a broad range of pesticides, representing several different chemical classes, induce variable toxic effects in aquatic species. The effects observed include diverse morphological malformations as well as physiological and behavioral effects. When development malformations occur, the myoskeletal system is among the most highly sensitive of targets. Myoskeletal effects that have been documented to result from pesticides were also known to interfere with the development of organ systems including the eyes or the heart and are also known to often cause lethal or sublethal edema in exposed organisms. The Physiological, behavioral, and population endpoints affected by pesticides include low or delayed hatching, growth suppression, as well as embryonal or larval mortality. The risks associated with pesticide exposure increase particularly during the spring. This is the period of time in which major pepticide applications take place, and this period unfortunately also coincides with many sensitive reproductive events such as spawning, egg laying, and early development of many aquatic organisms. Only few experimental studies with pesticides have directly linked developmental toxicity with key oxidative stress endpoints, such as lipid peroxidation, oxidative DNA damage, or modulation of antioxidant mechanisms. On the other hand, it has been documented in many reports that pesticide-related oxidative damage occurs in exposed adult fish, amphibians, and invertebrates. Moreover, the contribution of oxidative stress to the toxicity of pesticides has been emphasized in several recent review papers that have treated this topic. In conclusion, the available experimental data, augmented by several indirect lines of evidence, provide support to the concept that oxidative stress is a highly important mechanism in pesticide-induce reproductive or developmental toxicity. Other stressors may also act by oxidative mechanisms. This notwithstanding, there is much yet to learn about the details of this phenomenon and further research is needed to more fully elucidate the effects that pesticides have and the environmental risks they pose in the early development of aquatic organisms.

Ethanol-induced attenuation of oxidative stress is unable to alter mRNA expression pattern of catalase, glutathione reductase, glutathione-S-transferase (GST1A), and superoxide dismutase (SOD3) enzymes in Japanese rice fish (Oryzias latipes) embryogenesis

Although the mechanism of ethanol toxicity during embryogenesis is unknown, our earlier studies on Japanese rice fish (Oryzias latipes) embryos indicated that the effects might be mediated through oxidative stress. In this study we have determined the oxidative stress and the mRNA content of four antioxidant enzymes (catalase, glutathione reductase, glutathione-S-transferase, and superoxide dismutase) during Japanese rice fish embryogenesis (from 0 day post-fertilization to hatching) and after exposing the embryos to ethanol (100 and 300 mM) for 48 h at three stages (0-2, 1-3 and 4-6 days post-fertilization, dpf) of organogenesis. We observed that oxidative stress was minimal in blastula, gastrula or neurula stages, increased gradually with the advancement of morphogenesis and reached its maximum level in hatchlings. The antioxidant enzyme mRNAs were constitutively expressed throughout development; however, the expression pattern was not identical among the enzymes. Catalase and superoxide dismutase (SOD) mRNAs were minimal in the fertilized eggs, but increased significantly in 1 dpf and then either sharply dropped (SOD) or maintained a steady-state (catalase). Glutathione-S-transferase (GST) was very high in fertilized eggs and sharply dropped 1 dpf and then gradually increased thereafter. Glutathione reductase (GR) maintained a steady-state throughout the development. Ethanol was able to attenuate oxidative stress in embryos exposed only to 300 mM 1-3 dpf; no significant difference with controls was observed in other ethanol-treated groups. The antioxidant enzyme mRNAs also remained unaltered after ethanol treatment. From these data we conclude that the attenuation of oxidative stress by ethanol is probably due to the inhibition of normal growth of the embryos rather than by inhibiting catalase, GST, GR or SOD-dependent activities.

Reactive Oxygen Species and Aging in Caenorhabditis elegans: Causal or Casual Relationship?

The free radical theory of aging proposes a causal relationship between reactive oxygen species (ROS) and aging. While it is clear that oxidative damage increases with age, its role in the aging process is uncertain. Testing the free radical theory of aging requires experimentally manipulating ROS production or detoxification and examining the resulting effects on lifespan. In this review, we examine the relationship between ROS and aging in the genetic model organism Caenorhabditis elegans, summarizing experiments using long-lived mutants, mutants with altered mitochondrial function, mutants with decreased antioxidant defenses, worms treated with antioxidant compounds, and worms exposed to different environmental conditions. While there is frequently a negative correlation between oxidative damage and lifespan, there are many examples in which they are uncoupled. Neither is resistance to oxidative stress sufficient for a long life nor are all long-lived mutants more resistant to oxidative stress. Similarly, sensitivity to oxidative stress does not necessarily shorten lifespan and is in fact compatible with long life. Overall, the data in C. elegans indicate that oxidative damage can be dissociated from aging in experimental situations.

Optogenetic in vivo cell manipulation in KillerRed-expressing zebrafish transgenics

Background

KillerRed (KR) is a novel photosensitizer that efficiently generates reactive oxygen species (ROS) in KR-expressing cells upon intense green or white light illumination in vitro, resulting in damage to their plasma membrane and cell death.

Results

We report an in vivo modification of this technique using a fluorescent microscope and membrane-tagged KR (mem-KR)-expressing transgenic zebrafish. We generated several stable zebrafish Tol2 transposon-mediated enhancer-trap (ET) transgenic lines expressing mem-KR (SqKR series), and mapped the transposon insertion sites. As mem-KR accumulates on the cell membrane and/or Golgi, it highlights cell bodies and extensions, and reveals details of cellular morphology. The photodynamic property of KR made it possible to damage cells expressing this protein in a dose-dependent manner. As a proof-of-principle, two zebrafish transgenic lines were used to affect cell viability and function: SqKR2 expresses mem-KR in the hindbrain rhombomeres 3 and 5, and elsewhere; SqKR15 expresses mem-KR in the heart and elsewhere. Photobleaching of KR by intense light in the heart of SqKR15 embryos at lower levels caused a reduction in pumping efficiency of the heart and pericardial edema and at higher levels - in cell death in the hindbrain of SqKR2 and in the heart of SqKR15 embryos.

Conclusions

An intense illumination of tissues expressing mem-KR affects cell viability and function in living zebrafish embryos. Hence, the zebrafish transgenics expressing mem-KR in a tissue-specific manner are useful tools for studying the biological effects of ROS.

The COP9 signalosome mediates transcriptional and metabolic response to hormones, oxidative stress protection and cell wall rearrangement during fungal development

The COP9 signalosome complex (CSN) is a crucial regulator of ubiquitin ligases. Defects in CSN result in embryonic impairment and death in higher eukaryotes, whereas the filamentous fungus Aspergillus nidulans survives without CSN, but is unable to complete sexual development. We investigated overall impact of CSN activity on A. nidulans cells by combined transcriptome, proteome and metabolome analysis. Absence of csn5/csnE affects transcription of at least 15% of genes during development, including numerous oxidoreductases. csnE deletion leads to changes in the fungal proteome indicating impaired redox regulation and hypersensitivity to oxidative stress. CSN promotes the formation of asexual spores by regulating developmental hormones produced by PpoA and PpoC dioxygenases. We identify more than 100 metabolites, including orsellinic acid derivatives, accumulating preferentially in the csnE mutant. We also show that CSN is required to activate glucanases and other cell wall recycling enzymes during development. These findings suggest a dual role for CSN during development: it is required early for protection against oxidative stress and hormone regulation and is later essential for control of the secondary metabolism and cell wall rearrangement.

Redox control in mammalian embryo development

The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.

The Roles of Reactive Oxygen Species Produced by Contact Allergens and Irritants in Monocyte-derived Dendritic Cells

BACKGROUND

Although reactive oxygen species (ROS) have been produced in both mouse bone marrow-derived dendritic cells (DCs) and XS-106 DCs by contact sensitizers and irritants in previous studies, the generation of ROS in human monocyte-derived DCs (MoDCs) and their role in contact hypersensitivity (CHS) has yet to be elucidated.

OBJECTIVE

The purpose of this study was to determine whether contact allergens and irritants induce ROS in MoDCs and, if so, to evaluate the role of contact allergen and irritant induced-ROS in MoDCs in CHS.

METHODS

Production of ROS was measured by 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H(2)DCFDA) assay. Surface CD86 and HLA-DR molecules were detected by flow cytometry. Protein carbonylation was detected by Western blotting.

RESULTS

ROS were produced by contact allergens such as dinitrochlorobenzene (DNCB) and thimerosal and the irritant benzalkonium chloride (BKC). DNCB-induced, but not BKC-induced, ROS increased surface CD86 and HLA-DR molecules on MoDCs and induced protein carbonylation. These changes were reduced in the presence of antioxidant N-acetyl cysteine.

CONCLUSION

Our results suggest that DNCB-induced ROS may be different from those induced by irritant BKC. The DNCB-induced ROS may be associated with the CHS response, because they activate surface molecules on DCs that are important for generating immune reactions.

Sirt3 protects in vitro-fertilized mouse preimplantation embryos against oxidative stress-induced p53-mediated developmental arrest

Sirtuins are a phylogenetically conserved NAD+-dependent protein deacetylase/ADP-ribosyltransferase family implicated in diverse biological processes. Several family members localize to mitochondria, the function of which is thought to determine the developmental potential of preimplantation embryos. We have therefore characterized the role of sirtuins in mouse preimplantation development under in vitro culture conditions. All sirtuin members were expressed in eggs, and their expression gradually decreased until the blastocyst stage. Treatment with sirtuin inhibitors resulted in increased intracellular ROS levels and decreased blastocyst formation. These effects were recapitulated by siRNA-induced knockdown of Sirt3, which is involved in mitochondrial energy metabolism, and in Sirt3-/- embryos. The antioxidant N-acetyl-L-cysteine and low-oxygen conditions rescued these adverse effects. When Sirt3-knockdown embryos were transferred to pseudopregnant mice after long-term culture, implantation and fetal growth rates were decreased, indicating that Sirt3-knockdown embryos were sensitive to in vitro conditions and that the effect was long lasting. Further experiments revealed that maternally derived Sirt3 was critical. Sirt3 inactivation increased mitochondrial ROS production, leading to p53 upregulation and changes in downstream gene expression. The inactivation of p53 improved the developmental outcome of Sirt3-knockdown embryos, indicating that the ROS-p53 pathway was responsible for the developmental defects. These results indicate that Sirt3 plays a protective role in preimplantation embryos against stress conditions during in vitro fertilization and culture.

Reactive oxygen species: A radical role in development?

Reactive oxygen species (ROS), mostly derived from mitochondrial activity, can damage various macromolecules and consequently cause cell death. This ROS activity has been characterized in vitro, and correlative evidence suggests a role in various pathological conditions. In addition to this passive ROS activity, ROS also participate in cell signaling processes, though the relevance of this function in vivo is poorly understood. Throughout development, elevated cell activity is probably accompanied by highly active metabolism and, consequently, the production of large amounts of ROS. To allow proper development, cells must protect themselves from these potentially damaging ROS. However, to what degree ROS could participate as signaling molecules controlling fundamental and developmentally relevant cellular processes such as proliferation, differentiation, and death is an open question. Here we discuss why available data do not yet provide conclusive evidence on the role of ROS in development, and we review recent methods to detect ROS in vivo and genetic strategies that can be exploited specifically to resolve these uncertainties.

Diapause termination and development of encysted Artemia embryos: roles for nitric oxide and hydrogen peroxide

Encysted embryos (cysts) of the brine shrimp Artemia undergo diapause, a state of profound dormancy and enhanced stress tolerance. Upon exposure to the appropriate physical stimulus diapause terminates and embryos resume development. The regulation of diapause termination and post-diapause development is poorly understood at the molecular level, prompting this study on the capacity of hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) to control these processes. Exposure to H(2)O(2) and NO, the latter generated by the use of three NO generators, promoted cyst development, emergence and hatching, effects nullified by catalase and the NO scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). The maximal effect of NO and H(2)O(2) on cyst development was achieved by 4 h of exposure to either chemical. NO was effective at a lower concentration than H(2)O(2) but more cysts developed in response to H(2)O(2). Promotion of development varied with incubation conditions, indicating for the first time a population of Artemia cysts potentially arrested in post-diapause and whose development was activated by either H(2)O(2) or NO. A second cyst sub-population, refractory to hatching after prolonged incubation, was considered to be in diapause, a condition broken by H(2)O(2) but not NO. These observations provide clues to the molecular mechanisms of diapause termination and development in Artemia, while enhancing the organism's value in aquaculture by affording a greater understanding of its growth and physiology.

Gene expression, metabolic regulation and stress tolerance during diapause

Diapause entails molecular, physiological and morphological remodeling of living animals, culminating in a dormant state characterized by enhanced stress tolerance. Molecular mechanisms driving diapause resemble those responsible for biochemical processes in proliferating cells and include transcriptional, post-transcriptional and post-translational processes. The results are directed gene expression, differential mRNA and protein accumulation and protein modifications, including those that occur in response to changes in cellular redox potential. Biochemical pathways switch, metabolic products change and energy production is adjusted. Changes to biosynthetic activities result for example in the synthesis of molecular chaperones, late embryogenesis abundant (LEA) proteins and protective coverings, all contributing to stress tolerance. The purpose of this review is to consider regulatory and mechanistic strategies that are potentially key to metabolic control and stress tolerance during diapause, while remembering that organisms undergoing diapause are as diverse as the processes itself. Some of the parameters described have well-established roles in diapause, whereas the evidence for others is cursory.

Sculpturing digit shape by cell death

Physiological cell death is a key mechanism that ensures appropriate development and maintenance of tissues and organs in multicellular organisms. Most structures in the vertebrate embryo exhibit defined areas of cell death at precise stages of development. In this regard the areas of interdigital cell death during limb development provide a paradigmatic model of massive cell death with an evident morphogenetic role in digit morphogenesis. Physiological cell death has been proposed to occur by apoptosis, cellular phenomena genetically controlled to orchestrate cell suicide following two main pathways, cytochrome C liberation from the mitochondria or activation of death receptors. Such pathways converge in the activation of cysteine proteases known as caspases, which execute the cell death program, leading to typical morphologic changes within the cell, termed apoptosis. According to these findings it would be expected that caspases loss of function experiments could cause inhibition of interdigital cell death promoting syndactyly phenotypes. A syndactyly phenotype is characterized by absence of digit freeing during development that, when caused by absence of interdigital cell death, is accompanied by the persistence of an interdigital membrane. However this situation has not been reported in any of the KO mice or chicken loss of function experiments ever performed. Moreover histological analysis of dying cells within the interdigit reveals the synchronic occurrence of different types of cell death. All these findings are indicative of caspase alternative and/or complementary mechanisms responsible for physiological interdigital cell death. Characterization of alternative cell death pathways is required to explain vertebrate morphogenesis. Today there is great interest in cell death via autophagy, which could substitute or act synergistically to the apoptotic pathway. Here we discuss what is known about physiological cell death in the developing interdigital tissue of vertebrate embryos, paying special attention to the avian species.

Profiling of superoxide dismutase isoenzymes in compartments of the developing bovine antral follicles

The antral follicle constitutes a complex and regulated ovarian microenvironment that influences oocyte quality. Oxidative stress is a cellular state that may play a role during folliculogenesis and oogenesis, although direct supporting evidence is currently lacking. We thus evaluated the expression of the three isoforms (SOD1, SOD2, and SOD3) of the enzymatic antioxidant superoxide dismutase in all the cellular (granulosa cells, cumulus cells, and oocytes) and extracellular (follicular fluid) compartments of the follicle. Comparisons were made in bovine ovaries across progressive stages of antral follicular development. Follicular fluid possessed increased amounts of SOD1, SOD2, and SOD3 in small antral follicles when compared with large antral follicles; concomitantly, total SOD activity was highest in follicular fluids from smaller diameter follicles. SOD1, SOD2, and SOD3 proteins were expressed in granulosa cells without any fluctuations in follicle sizes. All three SOD isoforms were present, but were distributed differently in oocytes from small, medium, or large antral follicles. Cumulus cells expressed high levels of SOD3, some SOD2, but no detectable SOD1. Our studies provide a temporal and spatial expression profile of the three SOD isoforms in the different compartments of the developing bovine antral follicles. These results lay the ground for future investigations into the potential regulation and roles of antioxidants during folliculogenesis and oogenesis.

Apoptosis and autophagy in rat cerebellar granule neuron death: Role of reactive oxygen species

Programmed cell death (PCD) has been defined as an active, controlled process in which cells participate in their own demise. Apoptosis, or type I PCD, has been widely characterized, both morphologically and biochemically. More recently, autophagy, the self-digesting mechanism involved in the removal of cytoplasmic long-lived proteins, has been involved in cell death, and type II PCD is defined as cell death occurring with autophagic features. Neurons can undergo more than one type of PCD as a backup mechanism when the traditional death pathway is inhibited or in response to a particular death-inducing stimulus. Reactive oxygen species (ROS) have been shown to be important signaling molecules in the execution of apoptosis and, more recently, in the autophagic pathway. In this work, we characterize apoptotic and autophagic cell death in rat cerebellar granule neuron (CGN) culture, a widespread model for the study of neuronal death. Potassium deprivation (K5) and staurosporine (STS) were used for death induction. We found apoptotic and autophagic features under both conditions. Caspase inhibition as well as autophagy inhibition by 3-methyl adenine decreased cell death. Moreover, CGN can undergo the alternative type of cell death when the other one is inhibited. An antioxidant or NADPH oxidase inhibitors delayed apoptosis and had no effect in autophagic features. Thus, we found that autophagy plays a role in cell death of CGN and that, when cells are treated with K5 or STS, both autophagy and ROS seem to promote apoptosis by independent mechanisms.

Developmental biology of gut-probiotic interaction

While our current knowledge of probiotic interaction in the developing gut remains poorly understood, emerging science is providing greater biological insight into their mechanism of action and therapeutic potential for human disease. Given their beneficial effects, probiotics remain promising agents in neonatal gastrointestinal disorders. Probiotics may restore or supply essential bacterial strains needed for gut maturation and homeostasis, particularly in hosts where this process has been disrupted. Here we highlight the unique characteristics of developing intestinal epithelia with a focus on gut development and colonization as well as the inflammatory propensity of immature epithelia. Additionally, we review potential mechanisms of beneficial probiotic interaction with immature intestinal epithelia including immunomodulation, upregulation of cytoprotective genes, prevention and regulation of apoptosis and maintenance of barrier function. Improved knowledge of gut-probiotic interaction in developing epithelia will allow for a better understanding of how probiotics exert their beneficial effects and help guide their therapeutic use.

Lactobacillus rhamnosus blocks inflammatory signaling in vivo via reactive oxygen species generation

Uncontrolled inflammatory responses in the immature gut may play a role in the pathogenesis of many intestinal inflammatory syndromes that present in newborns or children, such as necrotizing enterocolitis (NEC), idiopathic inflammatory bowel diseases (IBD), or infectious enteritis. Consistent with previous reports that murine intestinal function matures over the first 3 weeks of life, we show that inflammatory signaling in the neonatal mouse gut increases during postnatal maturation, with peak responses occurring at 2-3 weeks. Probiotic bacteria can block inflammatory responses in cultured epithelia by inducing the generation of reactive oxygen species (ROS), which inhibit NF-kappaB activation through oxidative inactivation of the key regulatory enzyme Ubc12. We now report for the first time that the probiotic Lactobacillus rhamnosus GG (LGG) can induce ROS generation in intestinal epithelia in vitro and in vivo. Intestines from immature mice gavage fed LGG exhibited increased GSH oxidation and cullin-1 deneddylation, reflecting local ROS generation and its resultant Ubc12 inactivation, respectively. Furthermore, prefeeding LGG prevented TNF-alpha-induced intestinal NF-kappaB activation. These studies indicate that LGG can reduce inflammatory signaling in immature intestines by inducing local ROS generation and may be a mechanism by which probiotic bacteria can prevent NEC in premature infants or reduce the severity of IBD in children.

Rifampicin-activated human pregnane X receptor and CYP3A4 induction enhance acetaminophen-induced toxicity

Acetaminophen (APAP) is safe at therapeutic levels but causes hepatotoxicity via N-acetyl-p-benzoquinone imine-induced oxidative stress upon overdose. To determine the effect of human (h) pregnane X receptor (PXR) activation and CYP3A4 induction on APAP-induced hepatotoxicity, mice humanized for PXR and CYP3A4 (TgCYP3A4/hPXR) were treated with APAP and rifampicin. Human PXR activation and CYP3A4 induction enhanced APAP-induced hepatotoxicity as revealed by hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities elevated in serum, and hepatic necrosis after coadministration of rifampicin and APAP, compared with APAP administration alone. In contrast, hPXR mice, wild-type mice, and Pxr-null mice exhibited significantly lower ALT/AST levels compared with TgCYP3A4/hPXR mice after APAP administration. Toxicity was coincident with depletion of hepatic glutathione and increased production of hydrogen peroxide, suggesting increased oxidative stress upon hPXR activation. Moreover, mRNA analysis demonstrated that CYP3A4 and other PXR target genes were significantly induced by rifampicin treatment. Urinary metabolomic analysis indicated that cysteine-APAP and its metabolite S-(5-acetylamino-2-hydroxyphenyl)mercaptopyruvic acid were the major contributors to the toxic phenotype. Quantification of plasma APAP metabolites indicated that the APAP dimer formed coincident with increased oxidative stress. In addition, serum metabolomics revealed reduction of lysophosphatidylcholine in the APAP-treated groups. These findings demonstrated that human PXR is involved in regulation of APAP-induced toxicity through CYP3A4-mediated hepatic metabolism of APAP in the presence of PXR ligands.

Oxygen toxicity and reactive oxygen species: the devil is in the details

Reactive oxygen species (ROS) serve as cell signaling molecules for normal biologic processes. However, the generation of ROS can also provoke damage to multiple cellular organelles and processes, which can ultimately disrupt normal physiology. An imbalance between the production of ROS and the antioxidant defenses that protect cells has been implicated in the pathogenesis of a variety of diseases, such as cancer, asthma, pulmonary hypertension, and retinopathy. The nature of the injury will ultimately depend on specific molecular interactions, cellular locations, and timing of the insult. This review will outline the origins of endogenous and exogenously generated ROS. The molecular, cellular, pathologic, and physiologic targets will then be discussed with a particular emphasis on aspects relevant to child development. Finally, antioxidant defenses that scavenge ROS and mitigate associated toxicities will be presented, with a discussion of potential therapeutic approaches for the prevention and/or treatment of human diseases using enzymatic and nonenzymatic antioxidants.

Do organellar genomes function as long-term redox damage sensors?

A small group of proteins that form core components of electron transfer complexes are consistently encoded by organellar genomes in multicellular organisms, suggesting functional constraint. These genomes are costly to maintain and vulnerable to mutation. We propose that they provide cell lineages with sensors of long-term redox damage, and of bioenergetic and genomic competence. This proposed adaptive function sets tonic retrograde signalling to the nucleus and anterograde responses influencing protective and cell death pathways. The nature of the proposed gain-of-function signalling mechanisms is unclear but could involve defective complex assembly. Organellar proteomes therefore provide cumulative feedback on bioenergetic and genomic status within cell lineages, selection of the energetically 'fittest' cells and a means of removing cells that compromise survival of the organism.

Redox changes during the legume-rhizobium symbiosis

Reactive Oxygen Species (ROS) are continuously produced as a result of aerobic metabolism or in response to biotic and abiotic stresses. ROS are not only toxic by-products of aerobic metabolism, but are also signaling molecules involved in plant growth and environmental adaptation. Antioxidants can protect the cell from oxidative damage by scavenging the ROS. Thus, they play an important role in optimizing cell function by regulating cellular redox state and modifying gene expression. This article aims to review recent studies highlighting the role of redox signals in establishing and maintaining symbiosis between rhizobia and legumes.

Mitochondria and metazoan epigenesis

In eukaryotes, mitochondrial activity controls ATP production, calcium dynamics, and redox state, thereby establishing physiological parameters governing the transduction of biochemical signals that regulate nuclear gene expression. However, these activities are commonly assumed to fulfill a 'housekeeping' function: necessary for life, but an epiphenomenon devoid of causal agency in the developmental flow of genetic information. Moreover, it is difficult to perturb mitochondrial function without generally affecting cell viability. For these reasons little is known about the extent of mitochondrial influence on gene activity in early development. Recent discoveries pertaining to the redox regulation of key developmental signaling systems together with the fact that mitochondria are often asymmetrically distributed in animal embryos suggests that they may contribute spatial information underlying differential specification of cell fate. In many cases such asymmetries correlate with localization of genetic determinants (i.e., mRNAs or proteins), particularly in embryos that rely heavily on cell-autonomous means of cell fate specification. In such embryos the localized genetic determinants play a dominant role, and any developmental information contributed by the mitochondria themselves is likely to be less obvious and more difficult to isolate experimentally. Hence, 'regulative' embryos that make more extensive use of conditional cell fate specification are better suited to experimental investigation of mitochondrial impacts on developmental gene regulation. Recent studies of the sea urchin embryo, which is a paradigmatic example of such a system, suggest that anisotropic distribution of mitochondria provides a source gradient of spatial information that directs epigenetic specification of the secondary axis via Nodal-Lefty signaling.

Mitochondrial function and redox state in mammalian embryos

Mitochondria play a central and multifaceted role in the mammalian egg and early embryo, contributing to many different aspects of early development. While the contribution of mitochondria to energy production is fundamental, other roles for mitochondria are starting to emerge. Mitochondria are central to intracellular redox metabolism as they produce reactive oxygen species (ROS, the mediators of oxidative stress) and they can generate TCA cycle intermediates and reducing equivalents that are used in antioxidant defence. A high cytosolic lactate dehydrogenase activity coupled with dynamic levels of cytosolic pyruvate is responsible for a very dynamic intracellular redox state in the oocyte and embryo. Mammalian embryos have a low glucose metabolism during the earliest stages of development, as both glycolysis and the pentose phosphate pathway are suppressed. The mitochondrial TCA cycle is therefore the major source of reducing equivalents in the cytosol so that any change in mitochondrial function in the embryo will be reflected in changes in the intracellular redox state. In the mouse, the metabolic substrates used by the oocyte and early embryo each have a different impact on the intracellular redox state. Pyruvate which oxidises the cytosolic redox state, acts as an energetic and redox substrate whereas lactate, which reduces the cytosolic redox state, acts only as a redox substrate. Mammalian early embryos are very sensitive to oxidative stress which can cause permanent developmental arrest before zygotic genome activation and apoptosis in the blastocyst. The oocyte stockpiles antioxidant defence for the early embryo to cope with exogenous and endogenous oxidant insults arising during early development. Mitochondria provide ATP for glutathione (GSH) production during oocyte maturation and also participate in the regeneration of NADPH and GSH during early development. Finally, a number of pathological conditions or environmental insults impair early development by altering mitochondrial function, illustrating the centrality of mitochondrial function in embryo development.

Heme oxygenase and the cardiovascular-renal system

Heme oxygenase (HO) has been shown to be important for attenuating the overall production of reactive oxygen species (ROS) through its ability to degrade heme and to produce carbon monoxide (CO), biliverdin/bilirubin, and the release of free iron. Excess free heme catalyzes the formation of ROS, which may lead to endothelial cell (EC) dysfunction as seen in numerous pathological conditions including hypertension and diabetes, as well as ischemia/reperfusion injury. The upregulation of HO-1 can be achieved through the use of pharmaceutical agents, such as metalloporphyrins and some HMG-CoA reductase inhibitors. Among other agents, atrial natriretic peptide and donors of nitric oxide (NO) are important modulators of the heme-HO system, either through induction of HO-1 or the biological activity of its products. Gene therapy and gene transfer, including site- and organ-specific targeted gene transfer, have become powerful tools for studying the potential role of HO-1/HO-2 in the treatment of various cardiovascular diseases as well as diabetes. HO-1 induction by pharmacological agents or gene transfer of human HO-1 into endothelial cells (ECs) in vitro increases cell-cycle progression and attenuates Ang II, TNF-, and heme-mediated DNA damage; administration in vivo acts to correct blood pressure elevation following Ang II exposure. Moreover, site-specific delivery of HO-1 to renal structures in spontaneously hypertensive rats (SHR), specifically to the medullary thick ascending limb of the loop of Henle (mTALH), has been shown to normalize blood pressure and provide protection to the mTAL against oxidative injury. In other cardiovascular situations, delivery of human HO-1 to hyperglycemic rats significantly lowers superoxide (O(2)(-)) levels and prevents EC damage and sloughing of vascular EC into the circulation. In addition, administration of human HO-1 to rats in advance of ischemia/reperfusion injury considerably reduces tissue damage. The ability to upregulate HO-1 through pharmacological means or through the use of gene therapy may offer therapeutic strategies for cardiovascular disease in the future. This review discusses the implications of HO-1 delivery during the early stages of cardiovascular system injury or in early vascular pathology and suggests that pharmacological agents that regulate HO activity or HO-1 gene delivery itself may become powerful tools for preventing the onset or progression of certain cardiovascular pathologies.