BMP controls nitric oxide-mediated regulation of cell numbers in the developing neural tube

From Neural Tube Formation Through the Differentiation of Spinal Cord Neurons: Ion Channels in Action During Neural Development

Ion channels are expressed throughout nervous system development. The type and diversity of conductances and gating mechanisms vary at different developmental stages and with the progressive maturational status of neural cells. The variety of ion channels allows for distinct signaling mechanisms in developing neural cells that in turn regulate the needed cellular processes taking place during each developmental period. These include neural cell proliferation and neuronal differentiation, which are crucial for developmental events ranging from the earliest steps of morphogenesis of the neural tube through the establishment of neuronal circuits. Here, we compile studies assessing the ontogeny of ionic currents in the developing nervous system. We then review work demonstrating a role for ion channels in neural tube formation, to underscore the necessity of the signaling downstream ion channels even at the earliest stages of neural development. We discuss the function of ion channels in neural cell proliferation and neuronal differentiation and conclude with how the regulation of all these morphogenetic and cellular processes by electrical activity enables the appropriate development of the nervous system and the establishment of functional circuits adapted to respond to a changing environment.

Say "no" to spinal cord injury: is nitric oxide an option for therapeutic strategies?

PURPOSE

a literature review was made to investigate the role of nitric oxide (NO) in spinal cord injury, a pathological condition that leads to motor, sensory, and autonomic deficit. Besides, we were interested in potential therapeutic strategies interfering with NO mechanism of secondary damage.

MATERIALS

A literature search using PubMed Medline database has been performed.

RESULTS

excessive NO production after spinal cord injury promotes oxidative damage perpetuating the injury causing neuronal loss at the injured site and in the surrounding area.

CONCLUSION

different therapeutic approaches for contrasting or avoiding NO secondary damage have been studied, these include nitric oxide synthase inhibitors, compounds that interfere with inducible NO synthase expression, and molecules working as antioxidant. Further studies are needed to explain the neuroprotective or cytotoxic role of the different isoforms of NO synthase and the other mediators that take part or influence the NO cascade. In this way, it would be possible to find new therapeutic targets and furthermore to extend the experimentation to humans.

Genetic association analyses of nitric oxide synthase genes and neural tube defects vary by phenotype

Neural tube defects (NTDs) are caused by improper neural tube closure during the early stages of embryonic development. NTDs are hypothesized to have a complex genetic origin and numerous candidate genes have been proposed. The nitric oxide synthase 3 (NOS3) G594T polymorphism has been implicated in risk for spina bifida, and interactions between that single nucleotide polymorphism (SNP) and the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism have also been observed. To evaluate other genetic variation in the NO pathway in the development of NTDs, we examined all three NOS genes: NOS1, NOS2, and NOS3. Using 3109 Caucasian samples in 745 families, we evaluated association in the overall dataset and within specific phenotypic subsets. Haplotype tagging SNPs in the NOS genes were tested for genetic association with NTD subtypes, both for main effects as well as for the presence of interactions with the MTHFR C677T polymorphism. Nominal main effect associations were found with all subtypes, across all three NOS genes, and interactions were observed between SNPs in all three NOS genes and MTHFR C677T. Unlike the previous report, the most significant associations in our dataset were with cranial subtypes and the AG genotype of rs4795067 in NOS2 (p = 0.0014) and the interaction between the rs9658490 G allele in NOS1 and MTHFR 677TT genotype (p = 0.0014). Our data extend the previous findings by implicating a role for all three NOS genes, independently and through interactions with MTHFR, in risk not only for spina bifida, but all NTD subtypes.

Role of nitric oxide in cerebellar development and function: focus on granule neurons

More than 20 years of research have firmly established important roles of the diffusible messenger molecule, nitric oxide (NO), in cerebellar development and function. Granule neurons are main players in every NO-related mechanism involving cerebellar function and dysfunction. Granule neurons are endowed with remarkable amounts of the Ca(2+)-dependent neuronal isoform of nitric oxide synthase and can directly respond to endogenously produced NO or induce responses in neighboring cells taking advantage of the high diffusibility of the molecule. Nitric oxide acts as a negative regulator of granule cell precursor proliferation and promotes survival and differentiation of these neurons. Nitric oxide is neuroprotective towards granule neurons challenged with toxic insults. Nitric oxide is a main regulator of bidirectional plasticity at parallel fiber-Purkinje neuron synapses, inducing long-term depression (LTD) or long-term potentiation (LTP) depending on postsynaptic Ca(2+) levels, thus playing a central role in cerebellar learning related to motor control. Granule neurons cooperate with glial cells, in particular with microglia, in the regulation of NO production through the respective forms of NOS present in the two cellular types. Aim of the present paper is to review the state of the art and the improvement of our understanding of NO functions in cerebellar granule neurons obtained during the last two decades and to outline possible future development of the research.

Agmatine-reduced collagen scar area accompanied with surface righting reflex recovery after complete transection spinal cord injury

STUDY DESIGN

Intended to investigate whether agmatine treatment reduces collagen scar area in mice subjected to spinal cord injury (SCI).

OBJECTIVE

The purpose of the present study is to demonstrate the protective effect of agmatine on complete transection SCI mice. SUMMARY OF BACK GROUND DATA: The deposition of collagen that occurs at the lesion site, during the SCI, was well known. Agmatine has been reported to exert neuroprotective effect in various stress models including central nervous system injuries. In the present investigation, we hypothesized that agmatine treatment could rescue the mice subjected to SCI.

METHODS

Complete SCI was made at the T9 level. Agmatine was dissolved in normal saline (100 mg/kg, Sigma, St. Louis, MO) and given intraperitoneally 5 minutes after complete transection daily for 4 weeks (agmatine-treated mice, n = 30). Controls received normal saline in the same manner (experimental control, n = 30). Surface righting reflex test, expression of bone morphogenetic protein-7 (BMP-7), TGFβ-2 (transforming growth factor β-2), and collagen scar area were measured and the results were compared with Mann-Whitney U test using SAS.

RESULTS

Agmatine treatment improved the surface righting reflex of mice at 4 weeks after SCI (P = 0.030). The collagen scar, physical barrier to axon regeneration, was noticeably diminished by agmatine treatment at 4 weeks after SCI (P = 0.001). The expression of BMP-7, which is considered both neuroprotective and neuroregenerative, was increased in agmatine treatment group compared with experimental control group in the early stages after SCI (P = 0.015 at 1 day after SCI; P = 0.010 at 3 days; P = 0.035 at 1 week; P = 0.826 at 2 weeks). The expression of TGFβ-2 correlated with the deposition of the collagen matrix at the lesion site was decreased with agmatine treatment at 1 and 2 weeks after SCI (P = 0.001 at 1 week; P = 0.002 at 2 weeks). Survival rate was found to be higher in agmatine treatment group than in the experimental control group for 4 weeks after SCI (P = 0.076).

CONCLUSION

These results suggest that agmatine treatment could support neuroregeneration by reducing the collagen scar area through decreasing the expression of TGFβ-2 and increasing the expression of BMP-7 after SCI. Especially, the improved surface righting reflex of agmatine-treated group proposes that agmatine treatment have the potency to facilitate functional recovery after SCI. However, the drug (agmatine) warrants further investigation in higher mammals.

Manipulation of host behavior by parasitic insects and insect parasites

Parasites often alter the behavior of their hosts in ways that are ultimately beneficial to the parasite or its offspring. Although the alteration of host behavior by parasites is a widespread phenomenon, the underlying neuronal mechanisms are only beginning to be understood. Here, we focus on recent advances in the study of behavioral manipulation via modulation of the host central nervous system. We elaborate on a few case studies, in which recently published data provide explanations for the neuronal basis of parasite-induced alteration of host behavior. Among these, we describe how a worm may influence the nervous system of its cricket host and manipulate the cricket into committing suicide by jumping into water. We then focus on Ampulex compressa, which uses an Alien-like strategy for the sake of its offspring. Unlike most venomous hunters, this wasp injects venom directly into specific cerebral regions of its cockroach prey. As a result of the sting, the cockroach remains alive but immobile, but not paralyzed, and serves to nourish the developing wasp larva.

Functional role of bone morphogenetic protein-4 in isolated canine parietal cells

Bone morphogenetic protein (BMP)-4 is an important regulator of cellular growth and differentiation. Expression of BMP-4 has been documented in the gastric mucosa. We reported that incubation of canine parietal cells with EGF for 72 h induced both parietal cell morphological transformation and inhibition of H(+)/K(+)-ATPase gene expression through MAPK-dependent mechanisms. We explored the role of BMP-4 in parietal cell maturation and differentiation. Moreover, we investigated if BMP-4 modulates the actions of EGF in parietal cells. H(+)/K(+)-ATPase gene expression was examined by Northern blots and quantitative RT-PCR. Acid production was assessed by measuring the uptake of [(14)C]aminopyrine. Parietal cell apoptosis was quantitated by Western blots with anti-cleaved caspase 3 antibodies and by counting the numbers of fragmented, propidium iodide-stained nuclei. MAPK activation and Smad1 phosphorylation were measured by Western blots with anti-phospho-MAPK and anti-phospho-Smad1 antibodies. Parietal cell morphology was examined by immunohistochemical staining of cells with anti-H(+)/K(+)-ATPase alpha-subunit antibodies. BMP-4 stimulated Smad1 phosphorylation and induced H(+)/K(+)-ATPase gene expression. BMP-4 attenuated EGF-mediated inhibition of H(+)/K(+)-ATPase gene expression and blocked EGF induction of both parietal cell morphological transformation and MAPK activation. Incubation of cells with BMP-4 enhanced histamine-stimulated [(14)C]aminopyrine uptake. BMP-4 had no effect on parietal cell apoptosis, whereas TGF-beta stimulated caspase-3 activation and nuclear fragmentation. In conclusion, BMP-4 promotes the induction and maintenance of a differentiated parietal cell phenotype. These findings may provide new clues for a better understanding of the mechanisms that regulate gastric epithelial cell growth and differentiation.

Role of nitric oxide in chick embryonic organogenesis and dysmorphogenesis

BACKGROUND

Nitric oxide (NO), produced by the nitric oxide synthase family of enzymes, mediates multiple signaling functions, and when unchecked, NO causes pathological damage. Exposure of embryos to a variety of teratogens, including carbon monoxide (CO), has been shown to increase reactive intermediates, such as NO, and recent work showed that either the excess or absence of NO caused morphological defects. While endogenous NO is known to regulate many adult tissues, its role during embryonic organogenesis and/or in mediating responses to teratogen exposure has not been explored.

METHODS

We have examined here the presence of NO during normal chick embryonic organogenesis, and investigated the teratogenicity of NO through the application of sodium nitroprusside (SNP), which mimics NO overproduction, and NG-monomethyl-L-arginine (L-NMMA), which inhibits endogenous NOS activity.

RESULTS

Topical treatment with SNP or L-NMMA for 18 h resulted in morphological defects, specifically in the neural tube and somites, which corresponded to sites of altered apoptosis. The location of NO was histochemically correlated with the observed morphological defects. Coadministration of SNP or L-NMMA with CO showed functional coregulation and interaction between NO and CO in chick embryonic development.

CONCLUSIONS

Our results showed that regulation of NO is essential for normal axial development, that sites of altered NO expression correlate to those of altered apoptosis and dysmorphogenesis, and that CO coadministration resulted in a rectification of normal NO expression. Collectively, these results suggest that alteration in endogenous NO/CO signaling is responsible, at least in part, for the observed NO-induced teratogenesis.

NO-cGMP signaling and regenerative medicine involving stem cells

Nitric oxide (NO) is a short lived diatomic free radical species synthesized by nitric oxide synthases (NOS). The physiological roles of NO depend on its local concentrations as well as availability and the nature of downstream target molecules. At low nanomolar concentrations, activation of soluble guanylyl cyclase (sGC) is the major event initiated by NO. The resulting elevation in the intracellular cyclic GMP (cGMP) levels serves as signals for regulating diverse cellular and physiological processes. The participation of NO and cGMP in diverse physiological processes is made possible through cell type specific spatio-temporal regulation of NO and cGMP synthesis and signal diversity downstream of cGMP achieved through specific target selection. Thus cyclic GMP directly regulates the activities of its downstream effectors such as Protein Kinase G (PKG), Cyclic Nucleotide Gated channels (CNG) and Cyclic nucleotide phosphodiesterases, which in turn regulate the activities of a number of proteins that are involved in regulating diverse cellular and physiological processes. Localization and activity of the NO-cGMP signaling pathway components are regulated by G-protein coupled receptors, receptor and non receptor tyrosine kinases, phosphatases and other signaling molecules. NO also serves as a powerful paracrine factor. At micromolar concentrations, NO reacts with superoxide anion to form reactive peroxinitrite, thereby leading to the oxidation of important cellular proteins. Extensive research efforts over the past two decades have shown that NO is an important modulator of axon outgrowth and guidance, synaptic plasticity, neural precursor proliferation as well as neuronal survival. Excessive NO production as that evoked by inflammatory signals has been identified as one of the major causative reasons for the pathogenesis of a number of neurodegenerative diseases such as ALS, Alzheimers and Parkinson diseases. Regenerative therapies involving transplantation of embryonic stem cells (ES cells) and ES cell derived lineage committed neural precursor cells have recently shown promising results in animal models of Parkinson disease (PD). Recent studies from our laboratory have shown that a functional NO-cGMP signaling system is operative early during the differentiation of embryonic stem cells. The cell type specific, spatio-temporally regulated NO-cGMP signaling pathways are well suited for inductive signals to use them for important cell fate decision making and lineage commitment processes. We believe that manipulating the NO-cGMP signaling system will be an important tool for large scale generation of lineage committed precursor cells to be used for regenerative therapies.

Cytosolic labile zinc: a marker for apoptosis in the developing rat brain

Cytosolic zinc accumulation was thought to occur specifically in neuronal death (necrosis) following acute injury. However, a recent study demonstrated that zinc accumulation also occurs in adult rat neurons undergoing apoptosis following target ablation, and in vitro experiments have shown that zinc accumulation may play a causal role in various forms of apoptosis. Here, we examined whether intraneuronal zinc accumulation occurs in central neurons undergoing apoptosis during development. Embryonic and newborn Sprague-Dawley rat brains were double-stained for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL) detection of apoptosis and immunohistochemical detection of stage-specific neuronal markers, such as nestin, proliferating cell nuclear antigen (PCNA), TuJ1 and neuronal nuclear specific protein (NeuN). The results revealed that apoptotic cell death occurred in neurons of diverse stages (neural stem cells, and dividing, young and adult neurons) throughout the brain during the embryonic and early postnatal periods. Further staining of brain sections with acid fuchsin or zinc-specific fluorescent dyes showed that all of the apoptotic neurons were acidophilic and contained labile zinc in their cell bodies. Cytosolic zinc accumulation was also observed in cultured cortical neurons undergoing staurosporine- or sodium nitroprusside (SNP)-induced apoptosis. In contrast, zinc chelation with CaEDTA or N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) reduced SNP-induced apoptosis but not staurosporine-induced apoptosis, indicating that cytosolic zinc accumulation does not play a causal role in all forms of apoptosis. Finally, the specific cytosolic zinc accumulation may have a practical application as a relatively simple marker for neurons undergoing developmental apoptosis.

Neural tube closure depends on nitric oxide synthase activity

Neural tube (NT) closure is a multifactorial process that involves yet unresolved molecular mechanisms. It had been shown previously that high levels of nitric oxide (NO) block the process of NT closure in the chick embryo by inhibiting methionine synthase (MS). The MS inhibition and its effect on NT closure could be alleviated by folic acid, suggesting the involvement of the folate-methionine pathway in the process. Here we test the hypothesis that endogenous nitric oxide synthase (NOS) activity regulates the MS activity required in the process of NT closure. The experiments described here reveal that NOS activity per se, is indeed critical for NT closure in the chick embryo. Inhibition of NOS activity with either 2,4-diamino-6-hydroxypyrimidine (DAHP), which blocks biosynthesis of the NOS co-factor tetrahydrobiopterin (BH4), or with calmidazolium, which blocks calcium-calmodulin binding to NOS, resulted in reduced MS activity and consequently ablated NT closure. Addition of BH4 or the calcium ionophore A23187 restored NOS and MS activities, resulting in NT closure. The results described here imply that NOS and MS activities can serve as functional markers in this developmental process as they are essential in the process of NT closure.