Antiproliferative effects of NO synthase products

The role of IFN-gamma in immune responses to viral infections of the central nervous system

Interferon (IFN)-gamma, is not only a marker of T(H)1 CD4, CD8 and natural killer (NK) cells, it is also a critical antiviral mediator which is central to the elimination of viruses from the CNS. In this review, we describe IFN-gamma, its receptor, signal transduction from receptor engagement, and antiviral downstream mediators. We demonstrate that although neurons are post-mitotic and non-renewing, they respond to IFN-gamma in a fashion similar to peripheral fibroblasts or lymphocytes. We have illustrated this review with details about studies on the role(s) of IFN-gamma in the pathogenesis of measles virus (MV), herpes simplex virus (HSV) type 1, and vesicular stomatitis virus (VSV) infections of the CNS. For VSV infection, IFN-gamma signals through Jaks 1 and 2 and STAT1 to activate (interferon regulatory factor) IRF-1; although viral protein synthesis is inhibited, PKR is not a critical mediator in the antiviral response to VSV in murine neurons. In contrast, induction of nitric oxide synthase (NOS) type 1 and its production of nitric oxide is essential in the elimination of viruses from neurons.

Selective expression of the NOS II isoform during mouse vestibulocochlear receptorgenesis

Based on in vitro studies, nitric oxide (NO) is reported to be involved in initial neuronal differentiation. In order to compare this finding with the situation in vivo, we have looked for the expression of the three NO synthase isoforms in the developing mouse vestibulocochlear system. From these isoforms only the inducible NOS II is expressed during inner ear development. Examination of a series of embryonic and early postnatal animals, up to postnatal day 6, reveals a maturation-dependent, monophasic expression of this isoform. Initial expression is observed by day 10 of gestation in nerve cells of the vestibolocochlear ganglion and on their fibres. By day 14 of gestation, these afferent fibres penetrate the epithelium of the prospective receptor fields making contact with early, differentiating immunoreactive cochlear hair cells and receptor cells of the macula and crista ampullaris. This receptor-cell-derived immunoreactivity vanished in differentiated sensory hair cells by postnatal day 6, when both the constitutive isoforms and subsequent activated members of the down stream second messenger cascade (guanylate cyclase/cGMP) of the adult mouse were not then detectable. The strict phasic expression of NOS-II, independent of the second messenger system mentioned above, implies that there is a unique role for the inducible NOS isoform in nerve cell differentiation, independent of the NO/guanylate cyclase/cGMP pathway.

Tyrosine kinases are involved with the expression of inducible nitric oxide synthase in human articular chondrocytes

The present study characterizes mechanisms involved with the induction of nitric oxide (NO) production, nitric oxide synthase (NOS) enzymatic activity and mRNA expression in human articular chondrocytes. Activation of chondrocytes with lipopolysaccharide (LPS) or IL-1 resulted in time- and dose-dependent increases in iNOS mRNA followed by increased NOS enzymatic activity and NO release. The protein tyrosine kinase (PTK) inhibitors herbimycin A or genistein reduced IL-1 or LPS-induced NO release and NOS enzymatic activity. This was associated with inhibition of iNOS mRNA expression as determined by reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. In contrast, inhibitors of protein kinase C (PKC) or protein kinase A (PKA) did not affect these responses. These results were confirmed in experiments with second messenger agonists where neither activation of PKC, nor increases in cyclic adenosine monophosphate (cAMP) or increased intracellular calcium levels were associated with the induction of iNOS mRNA or NO release. These results suggest that PKC, PKA and calcium-dependent signals are not required or sufficient for the stimulation of NO production. However, NO production is dependent on tyrosine kinases due to their role in the expression of iNOS mRNA.