Nitric Oxide/Cyclic GMP-Dependent Calcium Signalling Mediates IL-6- and TNF-α-Induced Expression of Glial Fibrillary Acid Protein

Astrocyte activation is characterized by hypertrophy with increased glial fibrillary acidic protein (GFAP), whose expression may involve pro-inflammatory cytokines. In this study, the effects of pro-inflammatory IL-6 and TNF-α and anti-inflammatory cytokines IL-4 and IL-10 on nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signalling, intracellular calcium concentration ([Ca2+]i) and GFAP expression were investigated. In human glioblastoma astrocytoma U-373 MG cells, IL-6 and TNF-α, but not IL-4 or IL-10, increased iNOS, cGMP, [Ca2+]i and GFAP expression. The inhibitors of iNOS (1400 W), soluble guanylyl cyclase (ODQ) and IP3 receptors (ryanodine and 2-APB) reversed the increase in cGMP or [Ca2+]i, respectively, and prevented GFAP expression. In rat striatal slices, IL-6 and TNF-α, at variance with IL-4 and IL-10, promoted a concentration-dependent increase in Ca2+ efflux, an effect prevented by 1400 W, ODQ and RY/2APB. These data were confirmed by in vivo studies, where IL-6, TNF-α or the NO donor DETA/NO injected in the striatum of anaesthetised rats increased cGMP levels and increased GFAP expression. The present findings point to NO/cGMP-dependent calcium signalling as part of the mechanism mediating IL-6- and TNF-α-induced GFAP expression. As this process plays a fundamental role in driving neurotoxicity, targeting NO/cGMP-dependent calcium signalling may constitute a new approach for therapeutic interventions in neurological disorders.