Selective expression of the NOS II isoform during mouse vestibulocochlear receptorgenesis

A specific, non-immune system-related isoform of the human inducible nitric oxide synthase is expressed during differentiation of human stem cells into various cell types

BACKGROUND

NOS2 expression is mostly found in bacteria-exposed or cytokine-treated tissues and is mostly connected to innate immune reactions. There are three isoforms of NOS2 (NOS2-1 to -3). In RNA-seq data sets, analyzing inflammatory gene expression, only expression of the NOS2-1 mRNA isoform is detected. However, the expression of NOS2 in differentiating human pluripotent stems (hPSCs) has not been analyzed yet.

METHODS

Public available RNA-seq databases were screened for data of hPSCs during differentiation to different target cells. An isoform specific algorithm was used to analyze NOS2 mRNA isoform expression. In addition, we differentiated four different human iPSC cell lines toward cortical neurons and analyzed NOS2 mRNA expression by qRT-PCR and 5'-RACE. The functionality of the NOS2-2 protein was analyzed by transient transfection of expression clones in human DLD1 cells and nitrate measurement in the supernatant of these cells.

RESULTS

In RNA-seq databases we detected a transient expression of the NOS2 mRNA during the differentiation of hPSCs to cardiomyocytes, chondrocytes, mesenchymal stromal cells, neurons, syncytiotrophoblast cells, and trophoblasts. NOS2 mRNA isoform specific analyses showed, that the transiently expressed NOS2 mRNA in differentiating hPSC (NOS2-2; "diff-iNOS") differ remarkably from the already described NOS2 transcript found in colon or induced islets (NOS2-1; "immuno-iNOS"). Also, analysis of the NOS2 mRNA- and protein expression during the differentiation of four different hiPSC lines towards cortical neurons showed a transient expression of the NOS2 mRNA and NOS2 protein on day 18 of the differentiation course. 5'-RACE experiments and isoform specific qRT-PCR analyses revealed that only the NOS2-2 mRNA isoform was expressed in these experiments. To analyze the functionality of the NOS2-2 protein, we transfected human DLD-1 cells with tetracycline inducible expression clones encoding the NOS2-1- or -2 coding sequence. After induction of the NOS2-1 or -2 mRNA expression by tetracycline a similar nitrate production was measured proofing the functionality of the NOS2-2 protein isoform.

CONCLUSIONS

Our data show that a differentiation specific NOS2 isoform (NOS2-2) is transiently expressed during differentiation of hPSC. Video Abstract.

Genetics of guanylyl cyclase pathways in the cochlea and their influence on hearing

Although hearing loss is the most common sensory deficit in Western societies, there are no successful pharmacological treatments for this disorder. Recent experiments have demonstrated that manipulation of intracellular cyclic guanosine monophosphate (cGMP) concentrations can have both beneficial and harmful effects on hearing. In this review, we will examine the role of cGMP as a key second messenger involved in many aspects of cochlear function and discuss the known functions of downstream effectors of cGMP in sound processing. The nitric oxide-stimulated soluble guanylyl cyclase system (sGC) and the two natriuretic peptide-stimulated particulate GCs (pGCs) will be more extensively covered because they have been studied most thoroughly. The cochlear GC systems are attractive targets for medical interventions that improve hearing while simultaneously representing an under investigated source of sensorineural hearing loss.

Hearing impairment, cochlear morphology, and peroxynitrite (ONOO(-)) formation in adult and aging NOS II knockout mice

CONCLUSION

Nitric oxide synthase (NOS) II induction is a protective mechanism against age-related degeneration of the cochlea.

OBJECTIVES

An induction of NOS II has been described in different inner ear pathologies. The objective was to examine the role of NOS II in age-related degeneration of the cochlea.

METHODS

The hearing ability in adult and aging NOS II knockout mice (KO) and their wildtype (WT) littermates was explored via auditory brainstem response (ABR) measurements. Inner ear morphological differences were studied with scanning electron microscopy (SEM). Immunohistochemistry was used to examine the induction of NOS II in the inner ear of aging WT mice. Expression of nitrotyrosin, a marker protein for the reactive oxygen species peroxynitrite, was compared between KO and WT mice using immunohistochemistry.

RESULTS

Adult KO mice exhibited a mild hearing impairment. WT mice showed an induction of NOS II after 6 months of age. Age-related hearing deterioration was accelerated in KO mice, which was accompanied by increased nitrotyrosin formation and outer hair cell loss.

Nitric oxide enhances Oct-4 expression in bone marrow stem cells and promotes endothelial differentiation

This study was designed to investigate the role of nitric oxide (NO) in bone marrow stem cells and their differentiation into endothelial cells in vitro. Adult mouse bone marrow multipotent progenitor cells (MAPCs) were used as the source of stem cells. Oct-4 expression (both mRNA and protein) was significantly increased by up to 68.0% in MAPCs when incubated with NO donors DETA-NONOate or sodium nitroprusside (SNP) in a concentration-dependant manner (n=3, P<0.05). However, the cell proliferation was dramatically decreased by over 3-folds when treated with DETA-NONOate or SNP for 48 h (n=3, P<0.05). When MAPCs were exposed to DETA-NONOate (100 microM) for the first 48 h during differentiation, the expression (both mRNA and protein) of vWF was significantly increased at day 14 in the differentiating cells. The effects of DETA-NONOate or SNP on cell proliferation, Oct-4 expression and endothelial differentiation of MAPCs were not affected by the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one or cGMP analog 8-Br-cGMP. These data indicate that NO may regulate both the pluripotency and differentiation of MAPCs via a cGMP-independent mechanism.

Norepinephrine protects cortical neurons against microglial-induced cell death

Interleukin-1 beta (IL-1beta) is one of the main cytokines involved in the inflammatory response; it has multiple effects that can contribute to cell damage, one of which is the upregulation of the inducible form of nitric oxide (NO) synthase (NOS2) in certain cell types. We demonstrated previously that in vivo, cortical microglial inflammatory responses were increased when noradrenaline (NE) levels were depleted, suggesting that NE can reduce microglial activation. In the present report, we examined the role of IL-1beta in neurotoxicity induced by microglial-conditioned media, and possible neuroprotective effects of NE. Incubation of cortical neurons with conditioned media (CM) obtained from lipopolysaccharide (LPS)-treated microglia induced neuronal NOS2 expression and increased neuronal cell death, and these responses were reduced if the neurons were coincubated with interleukin-1 receptor antagonist. Cotreatment of microglial cells with LPS plus NE potently blocked IL-1beta production and reduced the ability of the CM to induce neuronal NOS2 and cell death. These results suggest that microglial release of IL-1beta is an important activator of neuronal inflammatory responses, and that protective effects of NE upon neurons involve a reduction of microglial-derived IL-1beta.

Transient expression of NOS-II during development of the murine enteric nervous system

In the enteric nervous system, nitric oxide (NO) is regarded as an important messenger for the non-adrenergic and non-cholinergic neurotransmission. Synthesized mainly by the constitutive nitric oxide synthase (NOS) isoforms NOS I and NOS III, this molecule exerts prejunctional inhibitory effects in the submucosal plexus as well as relaxation of enteric smooth muscles. In order to elucidate the role for NO during enteric development, we looked for the expression of all three NOS-isoforms in the enteric nervous system during mouse development from E8 to E20 using immunohistochemistry. Starting around midgestation, a transient expression of the NOS-II isoform during the very early development of enteric neurones was detected in parallel to that of HNK-1 exclusively in the myenteric plexus. Similar to findings for other neuronal systems, NOS-I and NOS III isoforms could be traced starting significantly later to increase toward the end of embryonic development when NOS II immunoreactivity faded and a strong expression of the vasointestinal peptide could be detected. In contrast to the NOSII expression, the constitutive isoforms can also be detected in the submucosal plexus. Altogether, these findings suggest NOS-II to be exclusively involved during early steps of enteric nervous system development. Absence of downstream signalling elements, such as sGC and cGMP both in neurons and in enteric muscle until the end of the second third of gestation, may indicate different effects executed by NO during development, expressed by Ca(2+) -dependent and Ca(2+) -independent NOS isoforms.

Altered expression of inducible nitric oxide synthase (iNOS) in the cochlea

Using immunohistochemistry and Western blot, the expression of inducible nitric oxide synthase (iNOS) in the lateral wall and organ of Corti was examined in normal (unstimulated) and stimulated mice and guinea pigs. The stimuli were: (1). injection of bacterial lipopolysaccharide (LPS, 5 mg/ml) into the middle ear through the tympanic membrane and (2). exposure to a 110 dB SPL (A-weighted) broadband noise, 3 h/day, for three consecutive days. For the unstimulated condition, weak iNOS expression was found in the vascular endothelium, marginal cells, nerve fibers, stereocilia of hair cells and Hensen's cells of the organ of Corti. More intense iNOS fluorescence signals were observed in cochlear tissues (particularly in hair cells and stria vascularis marginal cells) in animals exposed to loud sound or treated with LPS. Although the precise roles of iNOS expression in normal cochlear function have yet to be determined, enhanced iNOS expression following noise exposure and LPS suggests its participation in cochlear pathophysiology, including noise- and inflammatory factor-induced hearing loss.

NOS-II is involved in early differentiation of murine cortical, retinal and ES cell-derived neurons-an immunocytochemical and functional approach

Nitric oxide (NO), a cell-derived highly diffusible and unstable gas is regarded to be involved in inter- and intracellular communication in the nervous system. Based on findings about the expression of the inducible NO synthase (NOS) isoform during development of early mouse olfactory as well as vestibulocochlear receptor neurons, we intended to prove a general role of this isoform for neuronal differentiation. Using immunohistochemical techniques, an exclusive expression of the inducible NOS-II isoform in early post-mitotic neurons of the developing mouse cortex and retina can be detected. In a pharmacological approach using cultures of the mouse cortex as well as embryonic stem cell-derived neural precursor cells, we investigated the functional role of NO on initial neuronal differentiation. Effects of NOS inhibitors and NO donors on the morphological differentiation were correlated with developmentally regulated calcium current densities, focusing on the effects of the specific NOS-II inhibitor GW 274150. Furthermore, involvement of the soluble guanylate cyclase (sGC)/cGMP signaling cascade was pharmacologically investigated. Our data indicate that while a specific block of NOS-II provokes a clear inhibition of neurite outgrowth formation as well as a decrease of calcium current densities, the inverse is true for exogenous NO donation. In line with lacking immunoreactivity for the sGC and cGMP there are only minor effects of compounds manipulating the sGC/cGMP pathway, suggesting the downstream sGC/cGMP pathway not to be essential in these early differentiation steps.

Nitric oxide synthase expression and function in embryonic and adult cardiomyocytes

Nitric oxide (NO) is an important signalling molecule that plays a relevant role in different cell systems, among them the adult heart. The effects of NO are primarily mediated through modulation of Ca(2+) homeostasis, myofibrillar contractility, and metabolic regulation in cardiomyocytes. Recent evidence also suggests an important role of NO for cardiomyogenesis by modulating proliferation and differentiation and regulating cardiac function. In the embryonic, but also the healthy and diseased, adult mammalian heart, the inducible (iNOS) and the endothelial (eNOS) nitric oxide synthases (NOS) are detected. However, the expression pattern of NO and its function differ during development. Furthermore, under pathophysiological conditions NOS expression can also change and cause impairment of cardiac performance and cytotoxic effects. The present review focuses on the role and function of NO during cardiomyogenesis, the mechanisms responsible for eNOS availability, and the paracrine effects of NO generated by cardiomyocytes.

Nitric oxide in the afferent synaptic transmission of the axolotl vestibular system

This study was performed using intracellular and multiunit extracellular recording techniques in order to characterize the role of nitric oxide in the afferent synaptic transmission of the vestibular system of the axolotl (Ambystoma tigrinum). Bath application of nitric oxide synthase inhibitors N(G)-nitro-L-arginine (0.01microM to 10microM) and N-nitro-L-arginine methyl ester hydrochloride (0.1microM to 1000microM) elicited a dose-dependent decrease in the basal discharge of the semicircular canal afferent fibers. N(G)-Nitro-L-arginine also diminished the response to mechanical stimuli. Moreover, N(G)-nitro-L-arginine (1microM) produced a hyperpolarization associated with a decrease in the spike discharge and diminished the frequency of the excitatory postsynaptic potentials on afferent fibers recorded intracellularly. Nitric oxide donors were also tested: (i) S-nitroso-N-acetyl-DL-penicillamine (0.1microM to 100microM) increased the basal discharge and the response to mechanical stimuli. At the maximum effective concentration (100microM) this drug affected neither the amplitude nor the frequency of the excitatory postsynaptic potentials. However, it slightly depolarized the afferent neurons and decreased their input resistance. (ii) 3-Morpholino-sydnonimine hydrochloride did not significantly affect the basal discharge or the mechanically evoked peak response of afferent neurons at any of the concentrations used (1microM to 1000microM). However, after 10min of perfusion in the bath, 1microM and 10microM 3-morpholino-sydnonimine hydrochloride significantly modified the baseline of the mechanically evoked response, producing an increase in the mean spike discharge of the afferent fibers. These results indicate that nitric oxide may have a facilitatory role on the basal discharge and on the response to mechanical stimuli of the vestibular afferent fibers. Thus, nitric oxide probably participates in the sensory coding and adaptative changes of vestibular input in normal and pathological conditions.

Expression and function of inducible nitric oxide synthase in neurons

Enzymatically derived nitric oxide (NO) has been implicated in numerous physiological and pathological processes in the brain. Whereas during development NO participates in developmental and maturation processes, excess NO production in the adult in response to inflammation, injury, or trauma participates in both cell death and repair. The expression and activity of the inducible isoform of NO synthase (iNOS) play a pivotal role in sustained and elevated NO release. Recent evidence suggests that neurons can respond to proinflammatory stimuli and take part in brain inflammation. Neuronal iNOS expression has been described in different experimental settings, including cytokine stimulation of neuronal cell lines and primary neurons in vitro as well as in animal models of stroke and neurodegeneration. This article outlines different conditions leading to iNOS gene transcription and expression in neurons and neuronal cells and highlights the potential impact on human brain inflammation and neurodegeneration.

Nitric oxide distribution and production in the guinea pig cochlea

Production sites and distribution of nitric oxide (NO) were detected in cochlear lateral wall tissue, the organ of Corti and in isolated outer hair cells (OHCs) from the guinea pig using the fluorescent dye, 4,5-diaminofluorescein diacetate. Fluorescent signal, indicating the presence of NO, was found in the afferent nerves and their putative endings near inner hair cells (IHCs) and putative efferent nerve endings near OHCs, the IHCs and OHCs, the endothelial cells of blood vessels of the spiral ligament, the stria vascularis, and the spiral blood vessels of the basilar membrane. An increased NO signal was observed following exposure to the substrate for NO, L-arginine, while exposure to NO synthase inhibitors resulted in a decrease in NO signal. Observation of OHCs at the subcellular level revealed differentially strong fluorescent signals at the locations of cuticular plate, the subcuticular plate region, the infranuclear region, and the region adjacent to the lateral wall. The findings indicate the presence of NO in the cochlea and suggest that NO may play an important role in both regulating vascular tone and mediating neurotransmission in guinea pig cochlea.