Requirement for nitric oxide in retinal neuronal cell death induced by activated Muller glial cells

Retinal Muller glial cells express the inducible isoform (-2) of nitric oxi de (NO) synthase (NOS) in vitro after stimulation by lipopolysaccharide (LP S) and interferon-gamma (lFN-gamma) or in vivo in some retinal pathologies. Because NO may have beneficial or detrimental effects in the retina, we ha ve Used cocultures of retinal neurons with retinal Muller glial (RMG) cells from mice disrupted for the gene of NOS-2 [NOS-2 (-/-)] to clarify the rol e of NO in retinal neurotoxicity. We first demonstrated that NO produced by activated RMG cells was not toxic for RMG cells themselves. Second, the NO released from LPS/IFN-gamma-stimulated RMG cells induced neuronal cell dea th, because no neuronal cell death has been observed in cocultures with RMG cells from NOS-2 (-/-) mice and because inhibition of NOS-2 induction by t ransforming growth factor-beta or blockade of NO release by different NOS i nhibitors prevented neuronal cell death. Addition of urate, a peroxynitrite scavenger, or superoxide dismutase partially prevented neuronal cell death induced by NO, whereas the presence of a poly(ADP-ribose) synthetase inhib itor, caspase inhibitors, or a guanylate cyclase inhibitor had no significa nt effect on cell death. These results demonstrated that a large release of NO from RMG cells is responsible for retinal neuronal cell death in vitro, suggesting a neurotoxic role for NO and peroxynitrite during retinal infla mmatory or degenerative diseases, where RMG cells were activated.