Interleukin-4 and interleukin-10 modulate nuclear factor κB activity and nitric oxide synthase-2 expression in Theiler's virus-infected brain astrocytes

Abstract

In brain astrocytes, nuclear factor ΚB ΚB) is activated by stimuli that produce cellular stress causing the expression of genes involved in defence, including the inducible nitric oxide synthase (NOS-2). Theiler's murine encephalomyelitis virus (TMEV) induces a persistent CNS infection and chronic immune-mediated demyelination, similar to human multiple sclerosis. The cytokines interleukin (IL)-4 and IL-10 inhibit the expression of proinflammatory cytokines, counteracting the inflammatory process. Our study reports that infection of cultured astrocytes with TMEV resulted in a time-dependent phosphorylation of IΚBα, degradation of IΚBα and IΚBβ, activation of NF-ΚB and expression of NOS-2. The proteasome inhibitor MG-132 blocked TMEV-induced nitrite accumulation, NOS-2 mRNA expression and phospho-IΚBα degradation, suggesting NF-ΚB-dependent NOS-2 expression. Pretreatment of astrocytes with IL-4 or IL-10 decreased p65 nuclear translocation, NF-ΚB binding activity and NOS-2 transcription. IL-4 and IL-10 caused an accumulation of IΚBα in TMEV-infected astrocytes without affecting IΚBβ levels. The IΚB kinase activity and the degradation rate of both IΚBs were not modified by either cytokine, suggesting de novo synthesis of IΚBα. Indeed, IL-4 or IL-10 up-regulated IΚBα mRNA levels after TMEV infection. Therefore, the accumulation of IΚBα might impair the translocation of the NF-ΚB to the nucleus, mediating the inhibition of NF-ΚB activity. Overall, these data suggest a novel mechanism of action of IL-4 and IL-10, which abrogates NOS-2 expression in viral-infected glial cells.