Nitric oxide: promoter or suppressor of programmed cell death?

Deciphering molecular regulation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) signalling networks in Oryza genus amid environmental stress

The Oryza genus, containing Oryza sativa L., is quintessential to sustain global food security. This genus has a lot of sophisticated molecular mechanisms to cope with environmental stress, particularly during vulnerable stages like flowering. Recent studies have found key involvements and genetic modifications that increase resilience to stress, including exogenous application of melatonin, allantoin, and trehalose as well as OsSAPK3 and OsAAI1 in the genetic realm. Due to climate change and anthropogenic reasons, there is a rise in sea level which raises a concern of salinity stress. It is tackled through osmotic adjustment and ion homeostasis, mediated by genes like P5CS, P5CR, GSH1, GSH2, and SPS, and ion transporters like NHX, NKT, and SKC, respectively. Oxidative damage is reduced by a complex action of antioxidants, scavenging RONS. A complex action of genes mediates cold stress with studies highlighting the roles of OsWRKY71, microRNA2871b, OsDOF1, and OsICE1. There is a need to research the mechanism of action of proteins like OsRbohA in ROS control and the action of regulatory genes in stress response. This is highly relevant due to the changing climate which will raise a lot of environmental changes that will adversely affect production and global food security if certain countermeasures are not taken. Overall, this study aims to unravel the molecular intricacies of ROS and RNS signaling networks in Oryza plants under stress conditions, with the ultimate goal of informing strategies for enhancing stress tolerance and crop performance in this important agricultural genus.

The Key Roles of ROS and RNS as a Signaling Molecule in Plant-Microbe Interactions

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play a pivotal role in the dynamic cell signaling systems in plants, even under biotic and abiotic stress conditions. Over the past two decades, various studies have endorsed the notion that these molecules can act as intracellular and intercellular signaling molecules at a very low concentration to control plant growth and development, symbiotic association, and defense mechanisms in response to biotic and abiotic stress conditions. However, the upsurge of ROS and RNS under stressful conditions can lead to cell damage, retarded growth, and delayed development of plants. As signaling molecules, ROS and RNS have gained great attention from plant scientists and have been studied under different developmental stages of plants. However, the role of RNS and RNS signaling in plant-microbe interactions is still unknown. Different organelles of plant cells contain the enzymes necessary for the formation of ROS and RNS as well as their scavengers, and the spatial and temporal positions of these enzymes determine the signaling pathways. In the present review, we aimed to report the production of ROS and RNS, their role as signaling molecules during plant-microbe interactions, and the antioxidant system as a balancing system in the synthesis and elimination of these species.

Autophagy alleviates indium-induced programmed cell death in wheat roots

Indium released in agroecosystems is becoming an emerging plant stressor, causing cellular damage and consequently crop yield losses. Previous studies have focused on indium-induced toxicity in plants, while plant adaptive responses to such emerging metal xenobiotics are poorly understood. Here, we explored the relationship of autophagy and programmed cell death (PCD) in wheat roots under indium stress. Indium treatment significantly decreased root activity and cell viability, and suppressed the length of root epidermal cells in the elongation zones. These symptoms may be associated with indium-induced PCD, as indium-stressed wheat roots displayed condensed and granular nuclei, increased number of TUNEL-positive nuclei, enhanced nuclear DNA fragmentation and caspase-3-like protease activity compared to untreated roots. Accordingly, indium enhanced the expression levels of TaMCA1 and TaMCA4, two major metacaspase genes mediated PCD in wheat plants. The enhanced expression of autophagy genes and formation of autophagosomes indicate that autophagy could regulate metabolic adaptation and repair stress-induced damage in wheat roots. Furthermore, reinforcing autophagy by activator rapamycin significantly decreased the number of TUNEL-positive nuclei and the activity of caspase-3-like protease, whereas inhibition of autophagy by 3-methyladenine aggravated diagnostic markers for PCD. These results together suggest that autophagy suppresses indium-induced PCD in wheat roots.

Nitric oxide, salicylic acid and oxidative stress: Is it a perfect equilateral triangle?

Nitric oxide (NO) is an endogenous free radical involved in the regulation of a wide array of physio-biochemical phenomena in plants. The biological activity of NO directly depend on its cellular concentration which usually changes under stress conditions, it participates in maintaining cellular redox equilibrium and regulating target checkpoints which control switches among development and stress. It is one of the key players in plant signalling and a plethora of evidence supports its crosstalk with other phytohormones. NO and salicylic acid (SA) cooperation is also of great physiological relevance, where NO modulates the immune response by regulating SA linked target proteins i.e., non-expressor of pathogenesis-related genes (NPR-1 and NPR-2) and Group D bZIP (basic leucine zipper domain transcription factor). Many experimental data suggest a functional cooperative role between NO and SA in mitigating the plant oxidative stress which suggests that these relationships could constitute a metabolic "equilateral triangle".

Role of Nitric Oxide in Plant Senescence

In plants senescence is the final stage of plant growth and development that ultimately leads to death. Plants experience age-related as well as stress-induced developmental ageing. Senescence involves significant changes at the transcriptional, post-translational and metabolomic levels. Furthermore, phytohormones also play a critical role in the programmed senescence of plants. Nitric oxide (NO) is a gaseous signalling molecule that regulates a plethora of physiological processes in plants. Its role in the control of ageing and senescence has just started to be elucidated. Here, we review the role of NO in the regulation of programmed cell death, seed ageing, fruit ripening and senescence. We also discuss the role of NO in the modulation of phytohormones during senescence and the significance of NO-ROS cross-talk during programmed cell death and senescence.

Cryopreserved-pollen viability is regulated by NO-induced programmed cell death

After cryopreservation, the NO content in pollen increased, inducing programmed cell death as a key reason for reduced viability. Low recovery of biomaterials after cryopreservation is a bottleneck that limits the application of this technology. At present, the mechanism of viability decline after cryopreservation is not fully understood. In this study, the effects of nitric oxide (NO) on programmed cell death (PCD) and its relationship with viability were investigated, using Paeonia lactiflora 'Fen Yu Nu' pollen with significantly decreased viability after cryopreservation. The results showed that: the activity of caspase-3-like and caspase-9-like protease and the apoptosis rate of pollen cells were significantly increased, the expression level of the promoting PCD (pro-PCD) genes was up-regulated, while the expression level of the inhibiting PCD (anti-PCD) genes was down-regulated after preservation in liquid nitrogen (LN); the NO content in pollen cells increased significantly after LN exposure. The correlation analysis showed that NO was significantly correlated with pollen viability and all indicators of PCD. The addition of a NO carrier SNP after LN storage reduced pollen viability, increased endogenous NO content, decreased mitochondrial membrane potential level, activated caspase-3-like and caspase-9-like protease in pollen cells, and increased cell apoptosis rate. The expression levels of pro-PCD genes PDCD2 and ATG8CL were significantly up-regulated, while the expression levels of anti-PCD genes DAD1, BI-1 and LSD1 were significantly down-regulated. The addition of NO scavenger c-PTIO improved pollen viability, and produced the opposite effect of sodium nitroferricyanide (III) dihydrate (SNP), but did not change the mitochondrial membrane potential. These results suggest that NO induced PCD during the cryopreservation of pollen, which was one of the reasons for the significant decrease of pollen viability after cryopreservation.

Plant susceptible responses: the underestimated side of plant-pathogen interactions

Plant susceptibility to pathogens is usually considered from the perspective of the loss of resistance. However, susceptibility cannot be equated with plant passivity since active host cooperation may be required for the pathogen to propagate and cause disease. This cooperation consists of the induction of reactions called susceptible responses that transform a plant from an autonomous biological unit into a component of a pathosystem. Induced susceptibility is scarcely discussed in the literature (at least compared to induced resistance) although this phenomenon has a fundamental impact on plant-pathogen interactions and disease progression. This review aims to summarize current knowledge on plant susceptible responses and their regulation. We highlight two main categories of susceptible responses according to their consequences and indicate the relevance of susceptible response-related studies to agricultural practice. We hope that this review will generate interest in this underestimated aspect of plant-pathogen interactions.

Myoglobin Protects Breast Cancer Cells Due to Its ROS and NO Scavenging Properties

Myoglobin (MB) is an oxygen-binding protein usually found in cardiac myocytes and skeletal muscle fibers. It may function as a temporary storage and transport protein for O₂ but could also have scavenging capacity for reactive oxygen and nitrogen species. In addition, MB has recently been identified as a hallmark in luminal breast cancer and was shown to be robustly induced under hypoxia. Cellular responses to hypoxia are regulated by the transcription factor hypoxia-inducible factor (HIF). For exploring the function of MB in breast cancer, we employed the human cell line MDA-MB-468. Cells were grown in monolayer or as 3D multicellular spheroids, which mimic the in vivo avascular tumor architecture and physiology with a heterogeneous cell population of proliferating cells in the rim and non-cycling or necrotic cells in the core region. This central necrosis was increased after MB knockdown, indicating a role for MB in hypoxic tumor regions. In addition, MB knockdown caused higher levels of HIF-1α protein after treatment with NO, which also plays an important role in cancer cell survival. MB knockdown also led to higher reactive oxygen species (ROS) levels in the cells after treatment with H₂O₂. To further explore the role of MB in cell survival, we performed RNA-Seq after MB knockdown and NO treatment. 1029 differentially expressed genes (DEGs), including 45 potential HIF-1 target genes, were annotated in regulatory pathways that modulate cellular function and maintenance, cell death and survival, and carbohydrate metabolism. Of these target genes, TMEFF1, TREX2, GLUT-1, MKNK-1, and RAB8B were significantly altered. Consistently, a decreased expression of GLUT-1, MKNK-1, and RAB8B after MB knockdown was confirmed by qPCR. All three genes of interest are often up regulated in cancer and correlate with a poor clinical outcome. Thus, our data indicate that myoglobin might influence the survival of breast cancer cells, possibly due to its ROS and NO scavenging properties and could be a valuable target for cancer therapy.

S-nitrosothiols and H2S donors: Potential chemo-therapeutic agents in cancer

Nitric Oxide (NO) and Hydrogen Sulfide (H2S) are components of an "interactome", which is defined as a redox system involving the interactions of RSS, RNS and ROS. Chemical interaction by these species is common and is characterized by one and two electron oxidation, nitrosylation, nitration and sulfuration/polysulfidation reactions. NO and H2S are gases that penetrate cell membranes, are synthesized by specific enzymes, are ubiquitous, regulate protein activities through post-translational modifications and participate in cell signaling. The two molecules at high concentrations compared to physiological concentrations may result in cellular damage particularly through their interaction with other reactive species. NO and H2S can interact with each other and form a variety of molecular species which may have constructive or destructive behavior depending on the cell type, the cellular environment (ex. oxygen tension, pH, redox state), where the products are produced and in what concentrations. Cross talk exists between NO and H2S, whereby they can influence the generation and signaling behavior of each other. Given the above mentioned properties of NO and H2S and studies in cancer cells and animal models employing NO and H2S donors that generate higher than physiological concentrations of NO and H2S and are effective in killing cancer cells but not normal cells, lend credence to the possibility of the utility of these donors in an approach to the treatment of cancer.

Chinese herb pair Paeoniae Radix Alba and Atractylodis Macrocephalae Rhizoma suppresses LPS-induced inflammatory response through inhibiting MAPK and NF-κB pathway

Background

The combination of Radix Paeoniae Alba (RPA) and Rhizoma Atractylodis Macrocephalae (RAM) has long been used as a classic herb pair for the treatment of gynecologic and gastrointestinal diseases, but the underlying mechanisms of the herb pair remain unknown. This study aims to explore the anti-inflammatory potentials of RPA–RAM herb pair and to elucidate the underlying mechanisms.

Methods

The bioactive parts of RPA–RAM were extracted and screened through the inhibitory effects against nitric oxide (NO) production. The effects of optimized RPA–RAM extracts (OPAE) on inflammation-associated mediators were investigated by Western blotting, real-time quantitative PCR (RT-qPCR), Enzyme-linked immunosorbent (ELISA) and immunofluorescence staining.

Results

OPAE potently suppressed the productions of NO, TNF-α, IL-6 and MCP-1 in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages, concentration-dependently inhibited protein level of inducible nitric oxide synthase (iNOS), dramatically downregulated mRNA expression of iNOS, TNF-α, IL-6 and MCP-1. In addition, OPAE significantly prevented phosphorylation and degradation of inhibitory kappa Bα (IκBα) and subsequently restrained the nuclear translocation of NF-κB p65. Pretreatment with OPAE also attenuated the LPS-induced phosphorylation of ERK, JNK and p38.

Conclusions

Our findings demonstrated that OPAE suppressed inflammatory responses in LPS-stimulated RAW 264.7 macrophages by decreasing critical molecules involved in MAPK and NF-κB pathway, suggesting that the herb pair could be a promising therapeutic candidate for inflammation-related diseases.

Electronic supplementary material

The online version of this article (10.1186/s13020-019-0224-2) contains supplementary material, which is available to authorized users.

Anti-inflammatory effect of diterpenes-enriched fractions from Pterodon polygalaeflorus through inhibition of macrophage migration and cytokine production

Objectives

To evaluate the anti-inflammatory potential of Pterodon polygalaeflorus hexane extract (HE) and its fractions on macrophage migration in vitro and in vivo.

Methods

Hexane extract from P. polygalaeflorus fruits was fractionated and yielded four fractions. RAW 264.7 cells were treated with samples to evaluate cell viability (MTT assay), cell migration (wound healing and transwell assays), CD14 expression (flow cytometry), iNOS and cytokine mRNA expression (RT-qPCR), NO (Griess reaction) and cytokine (ELISA) production. In vivo migration was evaluated on the thioglycollate-induced peritonitis model. Qualitative analysis was performed by GC-MS.

Key findings

All fractions inhibited the NO production by LPS-stimulated RAW 264.7 cells. Fr3 and Fr4 presented the lowest IC50 values. The expressions of iNOS and IL-1β, TNF-α and IL-10 cytokines were inhibited by Fr3 and Fr4, whereas the CD14 expression was only inhibited by Fr3. All the samples inhibited RAW 264.7 migration in the wound healing and transwell assays. Fr3 and Fr4 reduced the migration of Mac-1+Gr-1− cells to the peritoneum and presented in their compositions: 6α-hydroxy-7β-acetoxyvouacapan-17β-oate, methyl 6α,7β-dihydroxyvouacapan-17β-oate, methyl 6α-acetoxy-7β-hydroxyvouacapan-17β-oate, geranylgeraniol and 14,15-epoxy-geranylgeraniol.

Conclusions

The anti-inflammatory effects of Fr3 and Fr4 involve inhibition of cell migration, iNOS expression and NO production, cytokine expression (mRNA and proteins) and CD14 expression (Fr3).

Effects of ERK1/2 S-nitrosylation on ERK1/2 phosphorylation and cell survival in glioma cells

Aberrant activation of extracellular signal-regulated kinase 1/2 (ERK1/2) by phosphorylation modification can trigger tumor cell development in glioma. S-nitrosylation, which refers to the covalent addition of a nitric oxide (NO) group to a cysteine (Cys) thiol, is an important post-translational modification that occurs on numerous cancer-associated proteins. Protein S-nitrosylation can increase or decrease protein activity and stability, and subsequent signal transduction and cellular processes. However, the association between ERK1/2 S-nitrosylation and ERK1/2 phosphorylation, and the effects of ERK1 S-nitrosylation on glioma cell survival are currently unknown. U251 glioma cells were treated with NO donors sodium nitroprusside (SNP) or S-nitrosoglutathione (GSNO). CCK8 assay was used to assess the cell viability. NO levels in the medium were detected by Griess assay. Western blot analysis and biotin switch assay were employed to detect the ERK1/2 phosphorylation and S-nitrosylation. ERK1 wild-type and mutant plasmids were constructed, and used to transfect the U251 cells. Caspase-3 western blot analysis and flow cytometry were employed to assess cell apoptosis. The present study demonstrated that treatment with the NO donors SNP or GSNO led to an increase in ERK1/2 S-nitrosylation, and a reduction in ERK1/2 phosphorylation, which was accompanied by growth inhibition of U251 glioma cells. Mutational analysis demonstrated that Cys¹⁸³ was vital for S-nitrosylation of ERK1, and that preventing ERK1 S-nitrosylation by replacing Cys¹⁸³ with alanine partially reversed GSNO-induced cell apoptosis, and reductions in cell viability and ERK1/2 phosphorylation. In addition, increased ERK1/2 phosphorylation was associated with decreased ERK1/2 S-nitrosylation in human glioma tissues. These findings identified the relationship between ERK1/2 S-nitrosylation and phosphorylation in vitro and in vivo, and revealed a novel mechanism of ERK1/2 underlying tumor cell development and apoptotic resistance of glioma.

In vivo inhibition of polyamine oxidase by a spermine analogue, MDL-72527, in tomato exposed to sublethal and lethal salt stress

The spermine analogue N1,N4-bis-(2,3-butadienyl)-1,4-butanediamine (MDL-72527), an effective inhibitor of polyamine oxidases (PAOs), triggers a systemic response in tomato (Solanum lycopersicum L.) exposed to sublethal (100mM) and lethal (250mM) NaCl concentrations. The accumulation of free polyamines (PAs), the terminal oxidation of PAs by diamine oxidases (DAOs) and PAOs, and the production of H2O2 by PA oxidases depends on the intensity of salt stress. Spermidine and spermine content increased significantly under sublethal salt concentrations, but remained low under lethal salt stress. Along with increased expression of the selected SlDAO1 and SlPAO1 genes in the leaves and roots, respectively, DAO and PAO activities and their product, H2O2, increased and initiated cell death by irreversible loss of electrolytes at 250mM NaCl. MDL-72527 significantly increased spermine, spermidine and/or putrescine contents as a result of reduced activity of PA oxidases; furthermore, it inhibited H2O2 and NO production during salt treatment. These results indicate that PAO contributed to H2O2 and NO production under salt stress, and the terminal activities of DAO and PAO play a role in cell death induction at 250mM NaCl. However, the inhibition of PAO by MDL-72527 does not increase the salt tolerance of plants, since electrolyte leakage increased significantly in the presence of the inhibitor.

Hyaluronic Acid Nanohydrogel Loaded With Quercetin Alone or in Combination to a Macrolide Derivative of Rapamycin RAD001 (Everolimus) as a New Treatment for Hormone-Responsive Human Breast Cancer

The aim of this study is based on the evaluation of anticancer, anti-inflammatory activities, and cellular uptake of hyaluronic acid nanohydrogel of quercetin tested alone and in combination to a macrolide derivative of rapamycin RAD001 (everolimus) on hormone-responsive breast cancer cell line MCF-7. Biological investigations were focused on the receptor mediated cellular internalization of the nanohydrogel and its abilities to reduce secretion of several cytokines (IL-8, IL-6, IL-19), VEGF, and metalloproteases (MMP-2, MMP-9) under pro-inflammatory conditions. Nanohydrogel show a CD44 dependent endocytosis with evident time dependent cytoplasmatic accumulation with abilities to reduce secretion of all cytokines of ∼60% compared to untreated cells. Combination of formulated quercetin and everolimus leads to a synergistic cytotoxic effects with a Combination Index of 0.38. These results highlights the importance of synergistic effect of the hyaluronic acid nanohydrogel of quercetin with everolimus in the regulation of human breast cancer cell proliferation and emphasize the antitumor and anti-inflammatory properties of the nanocarrier. J. Cell. Physiol. 232: 2063-2074, 2017. © 2016 Wiley Periodicals, Inc.

Nitrate Reductase Regulates Plant Nitric Oxide Homeostasis

Nitrate reductase (NR) is a key enzyme for nitrogen acquisition by plants, algae, yeasts, and fungi. Nitrate, its main substrate, is required for signaling and is widely distributed in diverse tissues in plants. In addition, NR has been proposed as an important enzymatic source of nitric oxide (NO). Recently, NR has been shown to play a role in NO homeostasis by supplying electrons from NAD(P)H through its diaphorase/dehydrogenase domain both to a truncated hemoglobin THB1, which scavenges NO by its dioxygenase activity, and to the molybdoenzyme NO-forming nitrite reductase (NOFNiR) that is responsible for NO synthesis from nitrite. We review how NR may play a central role in plant biology by controlling the amounts of NO, a key signaling molecule in plant cells.

Nitric oxide triggers a transient metabolic reprogramming in Arabidopsis

Nitric oxide (NO) regulates plant growth and development as well as responses to stress that enhanced its endogenous production. Arabidopsis plants exposed to a pulse of exogenous NO gas were used for untargeted global metabolomic analyses thus allowing the identification of metabolic processes affected by NO. At early time points after treatment, NO scavenged superoxide anion and induced the nitration and the S-nitrosylation of proteins. These events preceded an extensive though transient metabolic reprogramming at 6 h after NO treatment, which included enhanced levels of polyamines, lipid catabolism and accumulation of phospholipids, chlorophyll breakdown, protein and nucleic acid turnover and increased content of sugars. Accordingly, lipid-related structures such as root cell membranes and leaf cuticle altered their permeability upon NO treatment. Besides, NO-treated plants displayed degradation of starch granules, which is consistent with the increased sugar content observed in the metabolomic survey. The metabolic profile was restored to baseline levels at 24 h post-treatment, thus pointing up the plasticity of plant metabolism in response to nitroxidative stress conditions.

Dying with Style: Death Decision in Plant Embryogenesis

Embryogenesis is a fascinating event during the plant life cycle encompassing several steps whereby the zygote develops into a fully developed embryo which, in angiosperms, is composed of an axis separating the apical meristems, and two cotyledons. Recapitulation of embryogenesis can also occur in vitro through somatic embryogenesis, where somatic cells are induced to form embryos, and androgenesis, in which embryos originate from immature male gametophytes. Besides cell division and differentiation, embryo patterning in vivo and in vitro requires the dismantling and selective elimination of cells and tissues via programmed cell death (PCD). While the manifestation of the death program has long been acknowledged in vivo, especially in relation to the elimination of the suspensor during the late phases of embryo development, PCD during in vitro embryogenesis has only been described in more recent years. Independent studies using the gymnosperm Norway spruce and the angiosperm maize have shown that the death program is crucial for the proper formation and further development of immature somatic embryos. This chapter summarizes the recent advances in the field of PCD during embryogenesis and proposes novel regulatory mechanisms activating the death program in plants.

Inhibition of NOS-NO System Prevents Autoimmune Orchitis Development in Rats: Relevance of NO Released by Testicular Macrophages in Germ Cell Apoptosis and Testosterone Secretion

Background

Although the testis is considered an immunoprivileged organ it can orchestrate immune responses against pathological insults such as infection and trauma. Experimental autoimmune orchitis (EAO) is a model of chronic inflammation whose main histopathological features it shares with human orchitis. In EAO an increased number of macrophages infiltrate the interstitium concomitantly with progressive germ cell degeneration and impaired steroidogenesis. Up-regulation of nitric oxide (NO)-NO synthase (NOS) system occurs, macrophages being the main producers of NO.

Objective

The aim of our study was to evaluate the role of NO-NOS system in orchitis development and determine the involvement of NO released by testicular macrophages on germ cell apoptosis and testosterone secretion.

Method and Results

EAO was induced in rats by immunization with testicular homogenate and adjuvants (E group) and a group of untreated normal rats (N) was also studied. Blockage of NOS by i.p. injection of E rats with a competitive inhibitor of NOS, L-NAME (8mg/kg), significantly reduced the incidence and severity of orchitis and lowered testicular nitrite content. L-NAME reduced germ cell apoptosis and restored intratesticular testosterone levels, without variations in serum LH. Co-culture of N testicular fragments with testicular macrophages obtained from EAO rats significantly increased germ cell apoptosis and testosterone secretion, whereas addition of L-NAME lowered both effects and reduced nitrite content. Incubation of testicular fragments from N rats with a NO donor DETA-NOnoate (DETA-NO) induced germ cell apoptosis through external and internal apoptotic pathways, an effect prevented by N-acetyl-L-cysteine (NAC). DETA-NO inhibited testosterone released from Leydig cells, whereas NAC (from 2.5 to 15 mM) did not prevent this effect.

Conclusions

We demonstrated that NO-NOS system is involved in the impairment of testicular function in orchitis. NO secreted mainly by testicular macrophages could promote oxidative stress inducing ST damage and interfering in Leydig cell function.

Molecular basis of hair cell loss

Mechanisms that lead to the death of hair cells are reviewed. Exposure to noise, the use of ototoxic drugs that damage the cochlea and old age are accompanied by hair cell death. Outer hair cells are often more susceptible than inner hair cells, partly because of an intrinsically greater susceptibility; high frequency cells are also more vulnerable. A common factor in hair cell loss following age-related changes and exposure to ototoxic drugs or high noise levels is the generation of reactive oxygen species, which can trigger intrinsic apoptosis (the mitochondrial pathway). However, hair cell death is sometimes produced via an extracellular signal pathway triggering extrinsic apoptosis. Necrosis and necroptosis also play a role and, in various situations in which cochlear damage occurs, a balance exists between these possible routes of cell death, with no one mechanism being exclusively activated. Finally, the numerous studies on these mechanisms of hair cell death have led to the identification of many potential therapeutic agents, some of which have been used to attempt to treat people exposed to damaging events, although clinical trials are not yet conclusive. Continued work in this area is likely to lead to clinical treatments that could be used to prevent or ameliorate hearing loss.

Diverse functional interactions between nitric oxide and abscisic acid in plant development and responses to stress

The extensive support for abscisic acid (ABA) involvement in the complex regulatory networks controlling stress responses and development in plants contrasts with the relatively recent role assigned to nitric oxide (NO). Because treatment with exogenous ABA leads to enhanced production of NO, it has been widely considered that NO participates downstream of ABA in controlling processes such as stomata movement, seed dormancy, and germination. However, data on leaf senescence and responses to stress suggest that the functional interaction between ABA and NO is more complex than previously thought, including not only cooperation but also antagonism. The functional relationship is probably determined by several factors including the time- and place-dependent pattern of accumulation of both molecules, the threshold levels, and the regulatory factors important for perception. These factors will determine the actions exerted by each regulator. Here, several examples of well-documented functional interactions between NO and ABA are analysed in light of the most recent reported data on seed dormancy and germination, stomata movements, leaf senescence, and responses to abiotic and biotic stresses.

Connexin and Pannexin hemichannels are regulated by redox potential

Connexins (Cxs) and Pannexins (Panxs) are two non-related protein families, having both the property to form hemichannels at the plasma membrane. There are 21 genes coding for different Cx based proteins and only 3 for Panx. Under physiological conditions, these hemichannels (Cxs and Panxs) present a low open probability, but when open, they allow the release of signaling molecules to the extracellular space. However, under pathological conditions, these hemichannels increase their open probability, inducing important lysis of metabolites, and ionic imbalance, which in turn induce the massive entry of Ca⁺² to the cell. Actually, it is well recognized that Cxs and Panxs based channels play an important role in several diseases and -in many cases- this is associated with an aberrant hemichannel opening. Hemichannel opening and closing are controlled by a plethora of signaling including changes of the voltage plasma membrane, protein-protein interactions, and several posttranslational modifications, including protein cleavage, phosphorylation, glycosylation, hydroxylation and S-nitrosylation, among others. In particular, it has been recently shown that the cellular redox status modulates the opening/closing and permeability of at least Cx43, Cx46, and Panx1 hemichannels. Thus, for example, the gaseous transmitter nitric oxide (NO) can induce the S-nitrosylation of these proteins modulating in turn several of their properties. The reason is that the redox status of a cell is fundamental to set their response to the environment and also plays an important role in several pathologies. In this review, I will discuss how NO and other molecules associated with redox signaling modulate Cxs and Panx hemichannels properties.

Nitric oxide-triggered remodeling of chloroplast bioenergetics and thylakoid proteins upon nitrogen starvation in Chlamydomonas reinhardtii

Starving microalgae for nitrogen sources is commonly used as a biotechnological tool to boost storage of reduced carbon into starch granules or lipid droplets, but the accompanying changes in bioenergetics have been little studied so far. Here, we report that the selective depletion of Rubisco and cytochrome b6f complex that occurs when Chlamydomonas reinhardtii is starved for nitrogen in the presence of acetate and under normoxic conditions is accompanied by a marked increase in chlororespiratory enzymes, which converts the photosynthetic thylakoid membrane into an intracellular matrix for oxidative catabolism of reductants. Cytochrome b6f subunits and most proteins specifically involved in their biogenesis are selectively degraded, mainly by the FtsH and Clp chloroplast proteases. This regulated degradation pathway does not require light, active photosynthesis, or state transitions but is prevented when respiration is impaired or under phototrophic conditions. We provide genetic and pharmacological evidence that NO production from intracellular nitrite governs this degradation pathway: Addition of a NO scavenger and of two distinct NO producers decrease and increase, respectively, the rate of cytochrome b6f degradation; NO-sensitive fluorescence probes, visualized by confocal microscopy, demonstrate that nitrogen-starved cells produce NO only when the cytochrome b6f degradation pathway is activated.

S-nitrosylation of ERK inhibits ERK phosphorylation and induces apoptosis

Extracellular signal-regulated kinase (ERK) belongs to the mitogen-activated protein kinases (MAPK) superfamily. Aberrant upregulation and activation of ERK cascades may often lead to tumor cell development. However, how ERK is involved in tumor progression is yet to be defined. In current study, we described that ERK undergoes S-nitrosylation by nitric oxide (NO). ERK S-nitrosylation inhibits its phosphorylation and triggers apoptotic program as verified by massive apoptosis in fluorescence staining. The proapoptotic effect of NO induced S-nitrosylation is reversed by NO scavenger Haemoglobin (HB). Furthermore, an S-nitrosylation dead ERK mutant C183A also demolishes the proapoptotic potential of NO and favors cell survival. Therefore, Cys¹⁸³ might be a potential S-nitrosylation site in ERK. In addition, S-nitrosylation is a general phenomenon that regulates ERK activity. These findings identify a novel link between NO-mediated S-nitrosylation and ERK regulation, which provide critical insights into the control of apoptosis and tumor development.

H2O2-induced leaf cell death and the crosstalk of reactive nitric/oxygen species

In plants, the chloroplast is the main reactive oxygen species (ROS) producing site under high light stress. Catalase (CAT), which decomposes hydrogen peroxide (H2 O2 ), is one of the controlling enzymes that maintains leaf redox homeostasis. The catalase mutants with reduced leaf catalase activity from different plant species exhibit an H2 O2 -induced leaf cell death phenotype. This phenotype was differently affected by light intensity or photoperiod, which may be caused by plant species, leaf redox status or growth conditions. In the rice CAT mutant nitric oxide excess 1 (noe1), higher H2 O2 levels induced the generation of nitric oxide (NO) and higher S-nitrosothiol (SNO) levels, suggesting that NO acts as an important endogenous mediator in H2 O2 -induced leaf cell death. As a free radical, NO could also react with other intracellular and extracellular targets and form a series of related molecules, collectively called reactive nitrogen species (RNS). Recent studies have revealed that both RNS and ROS are important partners in plant leaf cell death. Here, we summarize the recent progress on H2 O2 -induced leaf cell death and the crosstalk of RNS and ROS signals in the plant hypersensitive response (HR), leaf senescence, and other forms of leaf cell death triggered by diverse environmental conditions. [Formula: see text] [ Chengcai Chu (Corresponding author)].

Cross-talk of nitric oxide and reactive oxygen species in plant programed cell death

In plants, programed cell death (PCD) is an important mechanism to regulate multiple aspects of growth and development, as well as to remove damaged or infected cells during responses to environmental stresses and pathogen attacks. Under biotic and abiotic stresses, plant cells exhibit a rapid synthesis of nitric oxide (NO) and a parallel accumulation of reactive oxygen species (ROS). Frequently, these responses trigger a PCD process leading to an intrinsic execution of plant cells. The accumulating evidence suggests that both NO and ROS play key roles in PCD. These redox active small molecules can trigger cell death either independently or synergistically. Here we summarize the recent progress on the cross-talk of NO and ROS signals in the hypersensitive response, leaf senescence, and other kinds of plant PCD caused by diverse cues.

Pro-apoptotic effect of anti-β1-adrenergic receptor antibodies in periodontitis patients

An anti-β(1)-adrenergic antibody from the sera of periodontitis patients (anti-β(1)-AR IgG) against the second extracellular loop of the human β(1)-adrenoceptor (β(1)-AR) has been shown to cause rat atria apoptosis. The anti-β(1)-AR IgG binds and activates atria β(1)-AR, increasing the intracellular calcium concentration, which, in turn, activates caspases-3, -8, and -9. The β(1)-AR and the post-receptor activation of calcium/calmodulin (CaM) lead to increased inducible nitric oxide synthase (iNOS) activity, with an increase in cyclic GMP (cGMP) accumulation as well as increased JNK phosphorylation and cyclic AMP (cAMP) production. We also observed an apoptotic effect of anti-β(1)-AR IgG, with increased generation of PGE(2). Comparatively, xamoterol, an authentic β(1)-AR agonist, mimicked the autoantibody effect on rat atria β(1)-AR apoptosis. Our results suggest that autoantibodies from the sera of periodontitis patients bind and interact with rat atria β(1)-AR, provoking apoptosis. This implicates a series of modulatory cardiac signaling events that could alter normal heart function and may occur with chronic stimulation of the atria β(1)-AR, which could lead to heart failure. These results suggest an important link between periodontitis and cardiovascular disease.

Altered endometrial expression of endothelial nitric oxide synthase in women with unexplained recurrent miscarriage and infertility

Endothelial nitric oxide synthase (eNOS) has diverse roles in the female reproductive system including a role in blastocyst implantation. Aberrant expression of eNOS could therefore be significant in the pathogenesis of disorders of implantation. In this study, eNOS protein and mRNA levels in the endometrium of women with recurrent miscarriages, unexplained infertility and a control group were determined by compartmental quantitative immunohistochemistry and real-time reverse-transcription PCR. eNOS was found to be immunolocalized to all layers of the endometrium and vascular endothelium. eNOS protein was higher in glandular epithelium (P = 0.004) and luminal epithelium (P = 0.002), but not vascular endothelium and stroma, in women with recurrent miscarriage. Similarly, in women with unexplained infertility, eNOS was significantly higher (P < 0.03) in luminal epithelium but not in any other compartments compared with the control group. The levels of mRNA confirmed the protein data, demonstrating higher eNOS mRNA in the endometrium of women with recurrent miscarriage and unexplained infertility compared with controls. In conclusion, increased expression of eNOS in glandular and luminal epithelium of the endometrium in women with recurrent miscarriages and unexplained infertility suggests a detrimental effect of excess nitric oxide in endometrial receptivity and implantation.

Radical decisions in cancer: redox control of cell growth and death

Free radicals play a key role in many physiological decisions in cells. Since free radicals are toxic to cellular components, it is known that they cause DNA damage, contribute to DNA instability and mutation and thus favor carcinogenesis. However, nowadays it is assumed that free radicals play a further complex role in cancer. Low levels of free radicals and steady state levels of antioxidant enzymes are responsible for the fine tuning of redox status inside cells. A change in redox state is a way to modify the physiological status of the cell, in fact, a more reduced status is found in resting cells while a more oxidative status is associated with proliferative cells. The mechanisms by which redox status can change the proliferative activity of cancer cells are related to transcriptional and posttranscriptional modifications of proteins that play a critical role in cell cycle control. Since cancer cells show higher levels of free radicals compared with their normal counterparts, it is believed that the anti-oxidative stress mechanism is also increased in cancer cells. In fact, the levels of some of the most important antioxidant enzymes are elevated in advanced status of some types of tumors. Anti-cancer treatment is compromised by survival mechanisms in cancer cells and collateral damage in normal non-pathological tissues. Though some resistance mechanisms have been described, they do not yet explain why treatment of cancer fails in several tumors. Given that some antitumoral treatments are based on the generation of free radicals, we will discuss in this review the possible role of antioxidant enzymes in the survival mechanism in cancer cells and then, its participation in the failure of cancer treatments.

Nitric oxide and protein S-nitrosylation are integral to hydrogen peroxide-induced leaf cell death in rice

Nitric oxide (NO) is a key redox-active, small molecule involved in various aspects of plant growth and development. Here, we report the identification of an NO accumulation mutant, nitric oxide excess1 (noe1), in rice (Oryza sativa), the isolation of the corresponding gene, and the analysis of its role in NO-mediated leaf cell death. Map-based cloning revealed that NOE1 encoded a rice catalase, OsCATC. Furthermore, noe1 resulted in an increase of hydrogen peroxide (H(2)O(2)) in the leaves, which consequently promoted NO production via the activation of nitrate reductase. The removal of excess NO reduced cell death in both leaves and suspension cultures derived from noe1 plants, implicating NO as an important endogenous mediator of H(2)O(2)-induced leaf cell death. Reduction of intracellular S-nitrosothiol (SNO) levels, generated by overexpression of rice S-nitrosoglutathione reductase gene (GSNOR1), which regulates global levels of protein S-nitrosylation, alleviated leaf cell death in noe1 plants. Thus, S-nitrosylation was also involved in light-dependent leaf cell death in noe1. Utilizing the biotin-switch assay, nanoliquid chromatography, and tandem mass spectrometry, S-nitrosylated proteins were identified in both wild-type and noe1 plants. NO targets identified only in noe1 plants included glyceraldehyde 3-phosphate dehydrogenase and thioredoxin, which have been reported to be involved in S-nitrosylation-regulated cell death in animals. Collectively, our data suggest that both NO and SNOs are important mediators in the process of H(2)O(2)-induced leaf cell death in rice.

Homeostatic NMDA receptor down-regulation via brain derived neurotrophic factor and nitric oxide-dependent signalling in cortical but not in hippocampal neurons

Nitric oxide (NO) has been proposed to down-regulate NMDA receptors (NMDA-Rs) in a homeostatic manner. However, NMDA-R-dependent NO synthesis also can cause excitotoxic cell death. Using bicuculline-stimulated hippocampal and cortical cell cultures, we have addressed the role of the brain-derived neurotrophic factor-NO pathway in NMDA-R down-regulation. This pathway protected cortical cells from NMDA-induced death and led to NMDA-R inhibition. In contrast, no evidence was gained for the presence of this protective pathway in hippocampal neurons, in which NMDA-induced NO synthesis was confirmed to be toxic. Therefore, opposing effects of NO depended on the activation of different signalling pathways. The pathophysiological relevance of this observation was investigated in synaptosomes and post-synaptic densities isolated from rat hippocampi and cerebral cortices following kainic acid-induced status epilepticus. In cortical, but not in hippocampal synaptosomes, brain-derived neurotrophic factor induced NO synthesis and inhibited NMDA-R currents present in isolated post-synaptic densities. In conclusion, we identified a NO-dependent homeostatic response in the rat cerebral cortex induced by elevated activity. A low performance of this pathway in brain areas including the hippocampus may be related to their selective vulnerability in pathologies such as temporal lobe epilepsy.

Nitric oxide production is not required for dihydrosphingosine-induced cell death in tobacco BY-2 cells

Sphinganine or dihydrosphingosine (d18:0, DHS), one of the most abundant free sphingoid Long Chain Base (LCB) in plants, is known to induce a calcium dependent programmed cell death (PCD) in tobacco BY-2 cells. In addition, we have recently shown that DHS triggers a production of H2O2, via the activation of NADPH oxidase(s). However, this production of H2O2 is not correlated with the DHS-induced cell death but would rather be associated with basal cell defense mechanisms. In the present study, we extend our current knowledge of the DHS signaling pathway, by demonstrating that DHS also promotes a production of nitric oxide (NO) in tobacco BY-2 cells. As for H2O2, this NO production is not necessary for cell death induction.