Leptin induces nitric oxide synthase type II in C6 glioma cells: Role for nuclear factor-κB in hormone effect

Astrocytes in the CNS produce inflammatory mediators in response to several stimuli and cytokines. Here we investigated the in vitro effect of leptin on inducible nitric oxide synthase (iNOS) expression in a glioma cell line (C6). After hormone stimulation, culture media were analysed for accumulated stable oxidation products of NO (NO2− and NO3−, designated as NOx), cellular RNA was extracted to determine iNOS mRNA level by RT-PCR and cellular lysates were prepared for protein expression. Leptin induced a concentration-dependent increase of NO release, related to iNOS induction. This effect was potentiated by IFN-γ, or TNF-α, or IFN-γ plus IL-1β. Pyrrolidine dithiocarbammate (PDTC) and N-α-tosyl-l-lysine chloromethyl ketone (TLCK), two inhibitors of NF-κB activation, as well as the specific proteasome inhibitor MG132, blocked leptin-induced iNOS. The role of NF-κB was also confirmed by time course studies on degradation of IκB-α, which began to degrade 5 min after treatment with leptin and returned to basal level after 30–60 min. Pre-incubation of cells with MG132 inhibited leptin-induced IκB-α degradation. These results confirm the pro-inflammatory role of leptin and identify it as a potential up-regulator of cytokine-induced inflammatory response in the CNS.