Manganese potentiates nuclear factor-κB-dependent:: Expression of nitric oxide synthase 2 in astrocytes by activating soluble guanylate cyclase and extracellular responsive kinase signaling pathways

Inflammatory activation of glial cells is associated with neuronal injury in several degenerative movement disorders of the basal ganglia, including manganese neurotoxicity. Manganese (Mn) potentiates the effects of inflammatory cytokines on nuclear factor-kappa B (NF-kappa B)dependent expression of nitric oxide synthase 2 (NOS2) in astrocytes, but the signaling mechanisms underlying this effect have remained elusive. It was postulated in the present studies that direct stimulation of cGMP synthesis and activation of mitogen-activated protein (MAP) kinase signaling pathways underlies the capacity of Mn to augment NF-kappa B-dependent gene expression in astrocytes. Exposure of primary cortical astrocytes to a low concentration of Mn (10 mu M) potentiated expression of NOS2 mRNA and protein along with production of NO in response to interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF alpha), which was prevented by overexpression of dominant negative I kappa B alpha. Mn also potentiated IFN-gamma and TNF alpha-induced phosphorylation of extracellular response kinase (ERK), p38, and JNK, as well as cytokine-induced activation of a fluorescent NF-kappa B reporter construct in transgenic astrocytes. Activation of ERK preceded that of NF-kappa B and was required for maximal activation of NO synthesis. Independently of IFN gamma/TNF alpha Mn-stimulated synthesis of cGMP in astrocytes and inhibition of soluble guanylate cyclase (sGC) abolished the potentiating effect of Mn on MAP kinase phosphorylation, NF-kappa B activation, and production of NO. These data indicate that near-physiological concentrations of Mn potentiate cytokine-induced expression of NOS2 and production of NO in astrocytes via activation of sGC, which pro-motes ERK-dependent enhancement of NF-kappa B signaling. (C) 2008 Wiley-Liss, Inc.