Modification of the nitric oxide concentration regulates the development of the apoptosis in the eye retina

Using model elaborated it was shown that the retinal ischemia initiated the development of the apoptosis in the inner layers of the retina. Administration of NOS inhibitor prevented the development of the apoptosis in the retina. To ascertain if nitric oxide could induce the retinal apoptosis by itself the nontoxic donor of nitric oxide (dinitrosyl iron complex) was injected intravitreally. Administration of DNIC in low concentrations induced the development of the apoptosis in the same retinal layers as in ischemia. The injection of dinitrosyl iron complex at the higher concentration resulted in the decrease of the apoptosis level. Administration of dinitrosyl iron complex with excess of glutathione didn't lead to the development of the retinal apoptosis. The obtained data demonstrates the neurotoxic properties of the excess of nitric oxide in the retina.     

Synthesis of nitric oxide in the bovine retina.

In the absence of light, high concentrations of cGMP open ion channels in the plasma membranes of rod outer segments. The source of stimulation of retinal guanylate cyclase is not known. Nitric oxide is a potent stimulator of guanylate cyclase in other cell systems. The present data demonstrate that nitric oxide synthase, an enzyme responsible for the production of nitric oxide, is present in retina, and specifically in the rod outer segments. This enzyme uses L-arginine as a substrate and is NADPH- and calcium- dependent. L-arginine-derived nitric oxide may be a source of activation of guanylate cyclase in the retina.     

Cytochrome c-d regulates developmental apoptosis in the Drosophila retina

The role of cytochrome c (Cyt c) in caspase activation has largely been established from mammalian cell-culture studies, but much remains to be learned about its physiological relevance in situ. The role of Cyt c in invertebrates has been subject to considerable controversy. The Drosophila genome contains distinct cyt c genes: cyt c-p and cyt c-d. Loss of cyt c-p function causes embryonic lethality owing to a requirement of the gene for mitochondrial respiration. By contrast, cyt c-d mutants are viable but male sterile. Here, we show that cyt c-d regulates developmental apoptosis in the pupal eye. cyt c-d mutant retinas show a profound delay in the apoptosis of superfluous interommatidial cells and perimeter ommatidial cells. Furthermore, there is no apoptosis in mutant retinal tissues for the Drosophila homologues of apoptotic protease-activating factor 1 (Ark) and caspase 9 (Dronc). In addition, we found that cyt c-d--as with ark and dronc-regulates scutellar bristle number, which is known to depend on caspase activity. Collectively, our results indicate a role of Cyt c in caspase regulation of Drosophila somatic cells.     

Paracrine neuroprotective effect of nitric oxide in the developing retina

The retina of newborn rats consists of the ganglion cell layer (GCL), the inner plexiform layer (IPL), the inner nuclear layer (INL) containing amacrine cells and the neuroblastic layer (NBL). In retinal explants, the GCL enters cell death after sectioning of the optic nerve, whereas there is almost no cell death in the NBL. When protein synthesis is inhibited with anisomycin, cell death is blocked in the GCL and induced in the NBL. We tested the roles of nitric oxide (NO) on cell death in the retina in vitro. Either L-arginine, the substrate for NO synthase or the NO donor S:-nitroso-acetylpenicillamine (SNAP) blocked cell death induced by anisomycin in the NBL, but had no effect in the GCL. Sepiapterin, a precursor of the nitric oxide synthase (NOS)-cofactor tetrahydrobiopterin also had a protective effect against anisomycin. The use of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble form of guanylyl cyclase, showed that anti-apoptotic effect of SNAP is partially mediated by cGMP generated by activation of guanylyl cyclase. NADPH-diaphorase histochemistry stained cells only in the GCL and INL. Thus, the degenerative effect of anisomycin is observed within the NBL, whereas the localization of NOS is restricted to the GCL and INL. The protective effect of both the NO substrate and cofactor upon cell death induced by anisomycin in the NBL, indicates that NO produced by amacrine and ganglion cells is a paracrine modulator of cell death within the retinal tissue.     

Level of nitric oxide in the kidneys during apoptosis activation

The content of nitric oxide stable metabolites in a tissue of kidneys of rats in conditions of activation of apoptosis was investigated. Research was carried out in two models: acute renal failure and a hypertrophy of a unique kidney after a unilateral nephrectomy. Detection of apoptosis was carried out by definition of DNA fragmentation. Substantial increase of the nitric oxide stable metabolites contents is revealed at activation of apoptosis in both models. Change of a ratio of the contents of nitrite--anions in relation to the general contents of NO2- + NO3- is revealed, indicating the role of peroxide processes in effect of nitric oxide and its metabolites on the cell.     

Mitochondrial nitric oxide synthase regulates mitochondrial matrix pH.

Nitric oxide (nitrogen monoxide, NO) exerts a wide profile of its biological activities via regulation of respiration and respiration-dependent functions. The presence of nitric oxide synthase (NOS) in mitochondria (mtNOS) was recently reported by us (Ghafourifar and Richter, FEBS Lett. 418, 291-296, 1997) and others (Giulivi et al., J. Biol. Chem. 273, 11038-11043, 1998). Here we report that NO, provided by an NO donor as well as by mtNOS stimulation, regulates mitochondrial matrix pH, transmembrane potential and Ca2+ buffering capacity. Exogenously-added NO causes a dose-dependent matrix acidification. Also mtNOS stimulation, induced by loading mitochondria with Ca2+, causes mitochondrial matrix acidification and a drop in mitochondrial transmembrane potential. Inhibition of mtNOS's basal activity causes mitochondrial matrix alkalinization and provides a resistance to the sudden drop of mitochondrial transmembrane potential induced by mitochondrial Ca2+ uptake. We conclude that mtNOS plays a critical role in regulating mitochondrial delta(pH).     

Xenopus cadherin-6 regulates growth and epithelial development of the retina

Cadherins are crucial for tissue cohesion, separation of cell layers and cell migration during embryogenesis. To investigate the role of classical type II Xcadherin-6 (Xcad-6), we performed loss-of-function studies by morpholino oligonucleotide injections. This resulted in severe eye defects which could be rescued with murine cadherin-6. In the absence of Xcadherin-6, morphological alterations and a decrease in cell proliferation were observed with eye cup formation. Eye field transplantations of Xcadherin-6 depleted donors yielded grafts that failed to form a proper neuroepithelium in a wildtype environment. At later developmental stages Xcadherin-6 deficient eyes showed lamination defects in the outer neural retina, a reduced thickness of the ganglion cell layer (GCL) and a fragmented retina pigment epithelium (RPE). Thus, Xcadherin-6 is essential early in eye development for structural organization and growth of the neuroepithelium before it differentiates into neural retina and RPE.     

Morphology and synaptic connectivity of nitric oxide synthase-immunoreactive neurons in the guinea pig retina

Immunocytochemical methods with an antiserum against neuronal nitric oxide synthase (NOS) were applied to identify the morphology and synaptic connectivity of NOS-like immunoreactive neurons in the guinea pig retina. In the present study, two types of amacrine cells were labeled with anti-NOS antisera. Type 1 cells had large somata located in the inner nuclear layer (INL) with long, sparsely branched processes ramifying mainly in stratum 3 of the inner plexiform layer (IPL). The somata of type 2 cells (smaller diameters) were located in the INL. Some displaced amacrine cells in the ganglion cell layer were labeled. The soma size of the displaced amacrine cells was similar to that of the type 2 amacrine cells. However, processes originating from type 2 amacrine cells and displaced amacrine cells stratified mainly in strata 1 and 5, respectively. Some cone bipolar cells were weakly NOS-immunoreactive. The synaptic connectivity of NOS-like immunoreactive amacrine cells was identified in the IPL by electron microscopy. NOS-labeled amacrine cell processes received synaptic input from other amacrine cell processes and bipolar cell axon terminals in all strata of the IPL. The most frequent postsynaptic targets of NOS-immunoreactive amacrine cells were other amacrine cell processes. Cone bipolar cells were postsynaptic to NOS-labeled amacrine cells in all strata of the IPL. Labeled amacrine cells synapsing onto ganglion cells were found only in sublamina b. A few synaptic contacts were observed between labeled cell processes. In the outer plexiform layer, dendrites of labeled bipolar cells made basal contact with cone pedicles or formed a synaptic triad opposed to a synaptic ribbon of cone pedicles.     

c-Jun N-terminal kinase 2 phosphorylates endothelial nitric oxide synthase at serine 116 and regulates nitric oxide production

The c-Jun N-terminal kinases (JNKs) belonging to the mitogen-activated protein kinase (MAPK) superfamily play important roles in foam-cell formation, hypercholesterolemia-mediated endothelial dysfunction, and the development of obesity. Although decreased nitric oxide (NO) production via decreased phosphorylation of endothelial NO synthase at serine 1179 (eNOS-Ser(1179)) was reported to be partly involved in JNK2-derived endothelial dysfunction, JNK2 seems likely to be indirectly involved in this signaling pathway. Here, using bovine aortic endothelial cells, we examined whether JNK2 directly phosphorylated eNOS-Ser(116), a putative substrate site for the MAPK superfamily, and this phosphorylation resulted in decreased NO release. JNK inhibitor SP60012 increased NO release in a time- and dose-dependent manner, which was accompanied by increased eNOS-Ser(116) phosphorylation. Purified JNK2 directly phosphorylated eNOS-Ser(116)in vitro. Ectopic expression of dominant negative JNK2 repressed eNOS-Ser(116) phosphorylation and increased NO production. Coimmunoprecipitation and confocal microscopy studies revealed a colocalization of eNOS and JNK2. However, all these observed effects were not manifested when JNK1 probes were used. Overall, this study indicates that JNK2 is a physiological kinase responsible for eNOS-Ser(116) phosphorylation and regulates NO production.     

Computational insights on the competing effects of nitric oxide in regulating apoptosis

Despite the establishment of the important role of nitric oxide (NO) on apoptosis, a molecular-level understanding of the origin of its dichotomous pro- and anti-apoptotic effects has been elusive. We propose a new mathematical model for simulating the effects of nitric oxide (NO) on apoptosis. The new model integrates mitochondria-dependent apoptotic pathways with NO-related reactions, to gain insights into the regulatory effect of the reactive NO species N(2)O(3), non-heme iron nitrosyl species (FeL(n)NO), and peroxynitrite (ONOO(-)). The biochemical pathways of apoptosis coupled with NO-related reactions are described by ordinary differential equations using mass-action kinetics. In the absence of NO, the model predicts either cell survival or apoptosis (a bistable behavior) with shifts in the onset time of apoptotic response depending on the strength of extracellular stimuli. Computations demonstrate that the relative concentrations of anti- and pro-apoptotic reactive NO species, and their interplay with glutathione, determine the net anti- or pro-apoptotic effects at long time points. Interestingly, transient effects on apoptosis are also observed in these simulations, the duration of which may reach up to hours, despite the eventual convergence to an anti-apoptotic state. Our computations point to the importance of precise timing of NO production and external stimulation in determining the eventual pro- or anti-apoptotic role of NO.     

一氧化氮及在脑发育中的作用

一氧化氮(NO)是一种小分子气体,是生物体内第一个被证实的气体信息分子。自1988年Carthwaite首次提出在神经系统中的传导作用后,NO在神经系统中的作用越来越受到重视。NO具有脂溶性、在体内易扩散、半衰期短(只有数秒钟)等生物学特征。体内的NO是由一氧化氮合酶(NOS)以左旋精氨酸为底物催化生成。     

Mitochondria as targets of apoptosis regulation by nitric oxide

In addition to their vital role as the cell's power stations, mitochondria exert an important function in apoptosis. In response to most if not all apoptosis inducers, mitochondrial membranes are permeabilized, leading to the release of potentially toxic proteins, mostly from the intermembrane space to the rest of the cells. Such pro-apoptotic intermembrane proteins include the caspase-independent death effector AIF, as well as cytochrome c, which can trigger the activation of caspases, once it has reached the cytosol. The mitochondrial permeabilization process can be induced by a variety of different xenobiotics, via a direct effect on mitochondrial membranes. Alternatively, mitochondrial permeabilization can be induced by endogenous second messengers, which are elicited in response to stress. The permeabilization process is controlled by the mitochondrial permeability transition pore complex (PTPC), by proteins of the Bcl-2/Bax family, as well as by lipids and metabolites. Nitric oxide (NO) is one of the second messengers that can trigger apoptosis by inducing mitochondrial membrane permeabilization. This effect may involve a direct effect on the PTPC and/or indirect effects secondary to the NO-mediated inhibition of oxidative phosphorylation. This has far-reaching implications for the pathophysiology of NO.     

Caspase-mediated apoptosis in neuronal excitotoxicity triggered by nitric oxide.

BACKGROUND: Excitotoxicity and excess generation of nitric oxide (NO) are believed to be fundamental mechanisms in many acute and chronic neurodegenerative disorders. Disturbance of Ca2+ homeostasis and protein nitration/nitrosylation are key features in such conditions. Recently, a family of proteases collectively known as caspases has been implicated as common executor of a variety of death signals. In addition, overactivation of poly-(ADP-ribose) polymerase (PARP) has been observed in neuronal excitotoxicity. We therefore designed this study to investigate whether triggering of caspase activity and/or activation of PARP played a role in cerebellar granule cell (CGC) apoptosis elicited by peroxynitrite (ONOO-) or NO donors. MATERIALS AND METHODS: CGC from wild-type or PARP -/- mice were exposed to various nitric oxide donors. Caspase activation and its implications for membrane alterations, Ca2+ homeostasis, intracellular proteolysis, chromatin degradation, and cell death were investigated. RESULTS: CGC exposed to NO donors undergo apoptosis, which is mediated by excess synaptic release of excitotoxic mediators. This excitotoxic mechanism differs from direct NO toxicity in some other neuronal populations and does not involve PARP activation. Inhibition of caspases with different peptide substrates prevented cell death and the related features, including intracellular proteolysis, chromatin breakdown, and translocation of phosphatidylserine to the outer surface of the cell membrane. Increased Ca2+ influx following N-methyl-D-aspartate (NMDA) receptor (NMDA-R) activation was not inhibited by caspase inhibitors. CONCLUSIONS: In CGC, NO donors elicit apoptosis by a mechanism involving excitotoxic mediators, Ca2+ overload, and subsequent activation of caspases.     

Increasing nitric oxide content in Arabidopsis thaliana by expressing rat neuronal nitric oxide synthase resulted in enhanced stress tolerance

Nitric oxide (NO) plays essential roles in many physiological and developmental processes in plants, including biotic and abiotic stresses, which have adverse effects on agricultural production. However, due to the lack of findings regarding nitric oxide synthase (NOS), many difficulties arise in investigating the physiological roles of NO in vivo and thus its utilization for genetic engineering. Here, to explore the possibility of manipulating the endogenous NO level, rat neuronal NOS (nNOS) was expressed in Arabidopsis thaliana. The 35S::nNOS plants showed higher NOS activity and accumulation of NO using the fluorescent probe 3-amino, 4-aminomethyl-2', 7'-difluorescein, diacetate (DAF-FM DA) assay and the hemoglobin assay. Compared with the wild type, the 35S::nNOS plants displayed improved salt and drought tolerance, which was further confirmed by changes in physiological parameters including reduced water loss rate, reduced stomatal aperture, and altered proline and malondialdehyde content. Quantitative real-time PCR analyses revealed that the expression of several stress-regulated genes was up-regulated in the transgenic lines. Furthermore, the transgenic lines also showed enhanced disease resistance against Pseudomonas syringae pv. tomato (Pst) DC3000 by activating the expression of defense-related genes. In addition, we found that the 35S::nNOS lines flowered late by regulating the expression of CO, FLC and LFY genes. Together, these results demonstrated that it is a useful strategy to exploit the roles of plant NO in various processes by the expression of rat nNOS. The approach may also be useful for genetic engineering of crops with increased environmental adaptations.     

The roles of nitric oxide in murine cardiovascular development

Nitric oxide (NO) participates in a diverse array of biological functions in mammalian organ systems. Depending on the biochemical environment, the production of NO may result in cytoprotection or cytotoxicity. The paradoxical actions of NO arise from the complexities generated by the redox milieu, NO concentration/bioavailability, and tissue/cell context, which ultimately result in the wide range of regulatory roles observed. Additionally, in physiological versus pathological states, NO often displays diametrically opposing affects in several organ systems. Here, we will discuss the roles of NO during reproduction, organ system development, in particular, the cardiovascular system, and its potential implications in diabetes-induced fetal defects.     

Morphological and neurochemical diversity of neuronal nitric oxide synthase-positive amacrine cells in the turtle retina

By gently scraping off the surface of the lateral ventricles of adult bovine brains, we obtained sheets containing the ependymal layer and some attached sub-ependymal cells. Explants were cultured in serum-free medium or in two media enriched with 20% fetal calf serum or 20% adult bovine cerebrospinal fluid, and processed for different time intervals from 4 h to 60 days. For characterization of the ependymal cells we used antisera against S-100 protein, vimentin and glial fibrillary acidic protein (GFAP). For comparison, the ependyma of adult bovines and of fetuses from days 60 to 120 post coitum was studied in situ. The adult ependyma consisted of a ciliated, cuboid cell monolayer with short basal processes; it displayed S-100 immunoreactivity but only scarce deposits of vimentin and no GFAP. The fetal ependyma had the appearance of a pseudostratified epithelium with elongated nuclei and basal processes containing S-100 and vimentin from day 80 post coitum and GFAP from day 100 post coitum. In explants, no differences were seen between the three culture media; the ependyma became pseudostratified, developed basal processes and showed increasing amounts of S-100 and vimentin first, and subsequently also GFAP. These changes were concomitant with the onset of mitotic activity in the subependymal layer leading to the production of numerous cells. The morphological and immunocytochemical features of ependymal cells in cultured explants resembled those of fetal ependyma. Our results indicate that the culture of ependymal explants from adult bovine lateral ventricles is an useful model system for morphological and functional studies of the ependyma and for the analysis of cell proliferation in the subependymal layer.     

Mitochondrial nitric oxide synthase, oxidative stress and apoptosis

Nitric oxide (NO) exerts a wide range of its biological properties via its interaction with mitochondria. By competing with O(2), physiologically relevant concentrations of NO reversibly inhibit cytochrome oxidase and decrease O(2) consumption, in a manner resembling a pharmacological competitive antagonism. The inhibition regulates many cellular functions, by e.g., regulating the synthesis of ATP and the formation of mitochondrial transmembrane potential (Delta Psi). NO regulates the oxygen consumption of both the NO-producing and the neighboring cells; thus, it can serve as autoregulator and paracrine modulator of the respiration. On the other hand, NO reacts avidly with superoxide anion (O(2)(-)) to produce the powerful oxidizing agent, peroxynitrite (ONOO(-)) which affects mitochondrial functions mostly in an irreversible manner. How mitochondria and cells harmonize the reversible effects of NO versus the irreversible effects of ONOO(-) will be discussed in this review article. The exciting recent finding of mitochondrial NO synthase will also be discussed.     

Role of nitric oxide in the induction of apoptosis by smokeless tobacco extract

The suggested role of oxidative stress in the pathogenesis of heart failure is largely based on utilizing left heart failure models. The present study on rats evaluated changes in antioxidants as well as oxidative stress in relation to hemodynamic function subsequent to the right heart failure induced by monocrotaline (50 mg/kg, i.p.). During the post-injection period, monocrotaline (MCT)-treated rats demonstrated a persistent growth depression. Two to three weeks after the injection, MCT-treated rats showed signs of fatigue, peripheral cyanosis and dyspnea. In these rats, right heart hypertrophy was confirmed by a significant increase in right ventricular weight as well as right ventricle to body weight ratio. In MCT-treated rats, there was also a significant increase in right ventricular systolic as well as end diastolic pressures. No change in lung and liver wet/dry weight ratios between MCT-treated and control animals was observed. Based on the hemodynamic data as well as other clinical observations, the functional stage achieved was compensated heart failure. Myocardial antioxidant enzymes, catalase, glutathione peroxidase and superoxide dismutase, in the MCT-treated rats were not different compared to control rats. Vitamin E levels were significantly depressed in the RV and there was no change in retinol levels. There was a significant increase in lipid hydroperoxide concentrations in MCT-treated rats as compared to the control group. These data provide evidence that right heart failure is associated with an increase in oxidative stress.