Inhibition of i-NOS but not n-NOS protects rat primary cell cultures against MPP(+)-induced neuronal toxicity.

Nitrative stress is a key component of the pathogenic process in Parkinson's disease (PD), but the relative roles of constitutive neuronal nitric oxide synthase (n-NOS) and inducible nitric oxide synthase (i-NOS) in glial cells remain unresolved. We have investigated the effects of a range of concentrations of the selective n-NOS inhibitor ARR17477, and the selective i-NOS inhibitor 1400W, on MPP(+)-induced cell death in foetal ventral mesencephalic (VM) dopaminergic cultures. MPP(+) induced a loss of TH-positive neurones accompanied by an increase in immunoreactivity for GFAP and OX-6 as markers of astrocytes and activated microglia, respectively, and induced i-NOS immunoreactivity. Unexpectedly, MPP(+) treatment did not induce 3-NT immunoreactivity in the cultures. ARR17477 and 1400W alone had no effect on the number of TH-positive cells or on the number of GFAP or OX-6 positive cells. ARR17477 did not prevent the MPP(+)-induced decrease in TH-positive neurones and had no effect on the increased number of GFAP- and OX-6-positive cells. By contrast, 1400W caused a concentration-dependent preservation of TH-positive neurones in the presence of MPP(+). It also significantly reduced the number of OX-6-immunoreactive cells and there was a small reduction in GFAP immunoreactivity. The results suggest a major role for i-NOS-mediated nitrative stress in microglia in MPP(+)-induced dopaminergic cell death and this may have important implications for developing neuroprotective strategies for PD.

The effect of nNOS inhibitors on toxin-induced cell death in dopaminergic cell lines depends on the extent of enzyme expression.

Nitric oxide is linked with neurodegeneration in Parkinson's disease (PD) through the involvement of both inducible (iNOS) and neuronal nitric oxide synthase (nNOS). While non-selective NOS inhibitors are neuroprotective, the role of nNOS has not been determined using selective NOS inhibitors. The present study investigated the neuroprotective effect of selective iNOS and nNOS inhibitors on MPP(+)- and MG-132-induced cell death in cell lines with differing levels of nNOS expression. Inhibition of endogenously expressed nNOS by 7-NI and ARR17477 enhanced the toxicity of MPP(+) and MG-132 in N1E-115 cells, whereas in transfected SH-SY5Y cells overexpressing nNOS, ARR17477 and 7-NI protected against MPP(+)- and MG-132-induced cell death. In contrast, inhibition of iNOS by 1400W was ineffective in preventing MPP(+) and MG-132 toxicity in these cell lines. These results suggest a dual role for NOS in dopaminergic cell viability. nNOS is protective against toxic insult when produced endogenously. When nNOS is overexpressed, it becomes neurotoxic to cells suggesting that inhibition of nNOS may be a promising strategy to prevent cell death in PD.

Combinations of genetic mutations in the adult neural stem cell compartment determine brain tumour phenotypes.

It has been suggested that intrinsic brain tumours originate from a neural stem/progenitor cell population in the subventricular zone of the post-natal brain. However, the influence of the initial genetic mutation on the phenotype as well as the contribution of mature astrocytes to the formation of brain tumours is still not understood. We deleted Rb/p53, Rb/p53/PTEN or PTEN/p53 in adult subventricular stem cells; in ectopically neurografted stem cells; in mature parenchymal astrocytes and in transplanted astrocytes. We found that only stem cells, but not astrocytes, gave rise to brain tumours, independent of their location. This suggests a cell autonomous mechanism that enables stem cells to generate brain tumours, whereas mature astrocytes do not form brain tumours in adults. Recombination of PTEN/p53 gave rise to gliomas whereas deletion of Rb/p53 or Rb/p53/PTEN generated primitive neuroectodermal tumours (PNET), indicating an important role of an initial Rb loss in driving the PNET phenotype. Our study underlines an important role of stem cells and the relevance of initial genetic mutations in the pathogenesis and phenotype of brain tumours.