Spatiotemporal analysis of NO production upon NMDA and tetanic stimulation of the hippocampus

LTP suppression by protein synthesis inhibitors is NO-dependent

For several decades, the ability of protein synthesis inhibitors (PSI) to suppress the long-term potentiation (LTP) of hippocampal responses is known. It is considered that mechanisms of such impairment are related to a cessation of translation and a delayed depletion of the protein pool required for maintenance of synaptic plasticity. The present study demonstrates that cycloheximide or anisomycin applications reduce amplitudes of the field excitatory postsynaptic potentials as well as the presynaptically mediated form of plasticity, the paired-pulse facilitation after LTP induction in neurons of the CA1 area of hippocampus. We showed that nitric oxide signaling could be one of the pathways that cause the LTP decrease induced by cycloheximide or anisomycin. Inhibitor of the NO synthase, L-NNA or the NO scavenger, PTIO, rescued the late-phase LTP and restored the paired-pulse facilitation up to the control levels. For the first time we have directly measured the nitric oxide production induced by application of the translation blockers in hippocampal neurons using the NO-sensitive dye DAF-FM. Inhibitory analysis demonstrated that changes during protein synthesis blockade downstream the NO signaling cascade are cGMP-independent and apparently are implemented through degradation of target proteins. Prolonged application of the NO donor SNAP impaired the LTP maintenance in the same manner as PSI.

Characterisation and comparison of temporal release profiles of nitric oxide generating donors

•

Nitric oxide release profiles were characterised for commonly used donors.

•

Released NO differs greatly between donors and depends on storage conditions.

•

High release donors (NOC-5, PAPA NONOate) decay quickly.

•

SNP and GSNO show greater stability releasing consistent lower NO levels.

•

This comprehensive characterisation provides knowledge to define NO concentrations released in vitro.

Background

Nitric oxide (NO) is a vital signalling molecule in a variety of tissues including the neuronal, vascular and reproductive system. However, its high diffusibility and inactivation make characterisation of nitrergic signalling difficult. The use of NO donors is essential to characterise downstream signalling pathways but knowledge of donor release capacities is lacking, thus making comparisons of donor responses difficult.

New method

This study characterises NO profiles of commonly used NO donors. Donors were stored under defined conditions and temporal release profiles detected to allow determination of released NO concentrations.

Results

Using NO-sensitive microsensors we assessed release profiles of NO donors following different storage times and conditions. We found that donors such as NOC-5 and PAPA-NONOate decayed substantially within days, whereas SNP and GSNO showed greater stability releasing consistent levels of NO over days. In all donors tested, the amount of released NO differs between frozen and unfrozen stocks.

Comparison with existing method(s)

Fluorescent and amperometric approaches to measure NO concentrations yield a wide range of levels. However, due to a lack of characterisation of the release profiles, inconsistent effects on NO signalling have been widely documented. Our systematic assessment of release profiles of a range of NO donors therefore provides new essential data allowing for improved and defined investigations of nitrergic signalling.

Conclusions

This is the first systematic comparison of temporal release profiles of different NO donors allowing researchers to compare conditions across different studies and the use of defined NO levels by choosing specific donors and concentrations.

Multimodality imaging of nitric oxide and nitric oxide synthases

Nitric oxide (NO) and NO synthases (NOSs) are crucial factors in many pathophysiological processes such as inflammation, vascular/neurological function, and many types of cancer. Noninvasive imaging of NO or NOS can provide new insights in understanding these diseases and facilitate the development of novel therapeutic strategies. In this review, we will summarize the current state-of-the-art multimodality imaging in detecting NO and NOSs, including optical (fluorescence, chemiluminescence, and bioluminescence), electron paramagnetic resonance (EPR), magnetic resonance (MR), and positron emission tomography (PET). With continued effort over the last several years, these noninvasive imaging techniques can now reveal the biodistribution of NO or NOS in living subjects with high fidelity which will greatly facilitate scientists/clinicians in the development of new drugs and/or patient management. Lastly, we will also discuss future directions/applications of NO/NOS imaging. Successful development of novel NO/NOS imaging agents with optimal in vivo stability and desirable pharmacokinetics for clinical translation will enable the maximum benefit in patient management.

The physiologic aggresome mediates cellular inactivation of iNOS

Nitric Oxide (NO), produced by inducible nitric oxide synthase (iNOS), has been implicated in the pathogenesis of various biological and inflammatory disorders. Recent evidence suggests that aggresome formation is a physiologic stress response not limited to misfolded proteins. That stress response, termed "physiologic aggresome," is exemplified by aggresome formation of iNOS, an important host defense protein. The functional significance of cellular formation of the iNOS aggresome is hitherto unknown. In this study, we used live cell imaging, fluorescence microscopy, and intracellular fluorescence NO probes to map the subcellular location of iNOS and NO under various conditions. We found that NO production colocalized with cytosolic iNOS but aggresomes containing iNOS were distinctly devoid of NO production. Further, cells expressing iNOS aggresomes produced significantly less NO as compared with cells not expressing aggresomes. Importantly, primary normal human bronchial epithelial cells, stimulated by cytokines to express iNOS, progressively sequestered iNOS to the aggresome, a process that correlated with marked reduction of NO production. These results suggest that bronchial epithelial cells used the physiologic aggresome mechanism for iNOS inactivation. Our studies reveal a novel cellular strategy to terminate NO production via formation of the iNOS aggresome.

Platelet-activating factor (PAF) increases NO production in human endothelial cells-real-time monitoring by DAR-4M AM

BACKGROUND

Platelet-activating factor (PAF) is a potent inflammatory lipid mediator that increases vascular permeability and vasodilation. Several studies have addressed the effect of PAF on nitric oxide (NO) production from microvessels in vivo.

OBJECTIVE

The aim of present study was to evaluate the effect of PAF on NO production in primary cultured human vascular endothelial cells.

METHODS

Human umbilical vein endothelial cells (HUVECs) were loaded with diaminorhodamine-4M acetoxymethyl ester (DAR-4MAM), and the cells were stimulated with PAF. Intracellular NO production was monitored as increase in fluorescence intensity. Also, NO production was visualized at cellular levels using DAR-4M AM and fluorescence imaging.

RESULTS

Significant increases in NO production in HUVECs were soon after the PAF stimulation, reaching a plateau after 10 min of the stimulation. The increase of NO production at 10 min after the stimulation was statistically significant (p<0.05) for 0.01-10 microM PAF. PAF-induced NO production was abolished by pretreatment of HUVECs with a NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA) or PAF receptor antagonist BN 52021. LysoPAF, the inactive metabolite of PAF, did not exert a significant effect on intracellular NO levels.

CONCLUSIONS

These results provide direct evidence that PAF cause intracellular NO production via activation of PAF receptors in human vascular endothelial cells.

Abnormal processing of tau in the brain of aged TgCRND8 mice

Amyloid plaques and neurofibrillary tangles are the main histopathological hallmarks of Alzheimer's disease (AD). In the neocortex and hippocampus of aged TgCRND8 mice, tau is hyperphosphorylated at different sites recognized by PHF-1, AT100, AT8 and CP13 antibodies. Phospho-SAPK/JNK levels were increased in the tg mouse brain, where activated SAPK/JNK co-localizes with PHF-1-positive cells. Phosphorylated tau-positive cells showed Bielschowsky- and Thioflavine S-positive intraneuronal deposits. PHF-1 and nitrotyrosine immunoreactivity merged within neurons surrounding amyloid deposits in cortical and hippocampal areas and immunoprecipitation studies confirmed that tau is nitrosylated. Our findings, demonstrating the presence of hyperphosphorylated and nitrosylated tau protein as well as of insoluble aggregates after the onset of amyloid deposition in the TgCRND8 mouse brain, indicate that the abnormal processing of tau may occur subsequently to cerebral amyloidosis and that activation of SAPK/JNK and induction of nitrosative stress are the more likely connecting factors between amyloidosis and tauopathy in AD.

Nitric oxide-dependent long-term potentiation revealed by real-time imaging of nitric oxide production and neuronal excitation in the dorsal horn of rat spinal cord slices

Nitric oxide (NO) is thought to be involved in the central mechanism of hyperalgesia and allodynia at the spinal level. Recently, we reported that NO played an important role in the induction of long-term potentiation (LTP) of synaptic strength in spinal dorsal horn, which is believed to underlie hyperalgesia and allodynia. In this study, to elucidate the relationship of NO to LTP in spinal dorsal horn, we measured the spatiotemporal distribution of NO signal with the NO-sensitive dye, DAR-4M, and neuronal excitation with the voltage-sensitive dye, RH482, in rat spinal cord slices, elicited by dorsal root stimulation. In superficial dorsal horn, neuronal excitation evoked by C fiber-activating dorsal root stimulation was potentiated for more than 2 h after low-frequency conditioning stimulation (LFS, 240 pulses at 2 Hz for 2 min). In the same slices that exhibited LTP, NO was produced and distributed in the superficial dorsal horn during the delivery of LFS, and the amplitude of LTP and amount of NO production showed close correlation from slice to slice. LTP and production of NO were inhibited in the presence of the NO synthase inhibitors and an inhibitor of heme oxygenase, the synthetic enzyme for carbon monoxide (CO). These results suggest that production and distribution of NO is necessary for the induction of LTP in spinal dorsal horn, and that CO contributes to the LTP induction and NO production by LFS.

Estradiol modulation of kainic acid-induced calcium elevation in neonatal hippocampal neurons

The developing hippocampus of both males and females is exposed to high levels of the gonadal steroid estradiol. The impact of this estradiol exposure on developing hippocampal neurons is essentially unknown. In the rat, the newborn hippocampus is relatively insensitive to excitotoxic brain injury, which in adults is associated with the release of amino acids, in particular glutamate, resulting in a significant increase in intracellular calcium and eventual cell death. We have shown previously in the rat that administration of the glutamate agonist, kainic acid (KA), on the day of birth results in limited hippocampal damage, which is ameliorated by treatment with the gonadal steroid, estradiol. We now show that KA induces an increase in intracellular calcium through L-type voltage-sensitive calcium channels early in development and, later in development, through polyamine-sensitive alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors with a modest increase through N-methyl-D-aspartate receptors. Pretreatment with the gonadal steroid, estradiol, decreases the percentage of neurons responding to KA and decreases the peak amplitude of the calcium transient early in development but has no effect later in development. Taken together, these data suggest that there is a developmental shift in the route of KA-induced intracellular calcium and estradiol modulates KA-induced intracellular calcium to a time restricted to early development, but whether this is the basis of the neuroprotective effect of estradiol remains to be determined.

Enhancement of nitric oxide production by association of nitric oxide synthase with N-methyl-D-aspartate receptors via postsynaptic density 95 in genetically engineered Chinese hamster ovary cells: real-time fluorescence imaging using nitric oxide sensitive dye

The current quantitative study demonstrates that the recruitment of neuronal nitric oxide synthase (nNOS) beneath N-methyl-D-aspartate (NMDA) receptors, via postsynaptic density 95 (PSD-95) proteins significantly enhances nitric oxide (NO) production. Real-time single-cell fluorescence imaging was applied to measure both NO production and Ca(2+) influx in Chinese hamster ovary (CHO) cells expressing recombinant NMDA receptors (NMDA-R), nNOS, and PSD-95. We examined the relationship between the rate of NO production and Ca(2+) influx via NMDA receptors using the NO-reactive fluorescent dye, diaminofluorescein-FM (DAF-FM) and the Ca(2+)-sensitive yellow cameleon 3.1 (YC3.1), conjugated with PSD-95 (PSD-95-YC3.1). The presence of PSD-95 enhanced the rate of NO production by 2.3-fold upon stimulation with 100 microm NMDA in CHO1(+) cells (expressing NMDA-R, nNOS and PSD-95) when compared with CHO1(-) cells (expressing NMDA-R and nNOS lacking PSD-95). The presence of nNOS inhibitor or NMDA-R blocker almost completely suppressed this NMDA-stimulated NO production. The Ca(2+) concentration beneath the NMDA-R, [Ca(2+)](NR), was determined to be 5.4 microm by stimulating CHO2 cells (expressing NMDA-R and PSD-95-YC3.1) with 100 microm NMDA. By completely permealizing CHO1 cells with ionomycin, a general relationship curve of the rate of NO production versus the Ca(2+) concentration around nNOS, [Ca(2+)](NOS), was obtained over the wide range of [Ca(2+)](NOS). This sigmoidal curve had an EC(50) of approximately 1.2 microm of [Ca(2+)](NOS), implying that [Ca(2+)](NR) = 5.4 microm can activate nNOS effectively.

Nitric oxide and metastatic cell behaviour

Nitric oxide (NO) is a pleiotropic signalling molecule that subserves a wide variety of basic cellular functions and also manifests itself pathophysiologically. As regards cancer and its progression, however, the reported role of NO appears surprisingly inconsistent. In this review, we focus on metastasis, the process of cancer cell spread and secondary tumour formation. In a 'reductionist' approach, we consider the metastatic cascade to be made up of a series of basic cellular behaviours (such as proliferation, apoptosis, adhesion, secretion migration, invasion and angiogenesis). We evaluate how NO controls such behaviours, in comparison with normal cells. The available information suggests strongly that NO signalling would be expected to regulate these behaviours both positively and negatively and this probably leads to the observed apparent variability in the NO status of cancer cells and tissues. Thus, the role of NO in cancer is more complex than previously thought. A number of suggestions are made, including consideration of novel mechanisms, such as ion channels, in order to achieve a more consistent and integrated understanding of NO signalling in cancer and to realise its clinical potential.