Double‐stranded RNA induces nitric oxide synthase in human astrocytes

Environmental factor(s), such as viral infection, has been implicated as one of the potential triggering events leading to demyelination in MS. This study underlines the importance of double-stranded RNA (dsRNA), the active component of a viral infection that stimulates antiviral responses in infected cells, in inducing the expression of inducible nitric oxide synthase (iNOS) in human astroglia. Treatment of human U373MG astroglial cells with dsRNA in the form of synthetic polyinosinic-polycytidylic acid (poly IC) induces the production of NO and the expression of iNOS in a dose-dependent manner. Similar to human U373MG astroglial cells, poly IC also induces the expression of iNOS in human primary astroglia. Induction of human iNOS promoter-derived luciferase activity by poly IC suggests that poly IC induces the transcription of iNOS. As activation of both NF-κB and C/EBPb is necessary for the transcription of iNOS in human astroglia, we investigated the effect of poly IC on the activation of both NF-κB and C/EBPb. Poly IC induced the activation of both NF-κB and C/EBPb. Furthermore, inhibition of poly IC-induced production of NO by Dp65, a dominant-negative mutant of p65, and DC/EBPb, a dominant-negative mutant of C/EBPb, suggests that poly IC induces the expression of iNOS in human astroglial cells through the activation of NF-κB and C/EBPb. This study delineates a novel role of dsRNA in inducing the expression of iNOS in human astroglia which may participate in virus-induced neurological abnormalities. Acknowledgements:  This study was supported by NIH grants (NS39940 and AG19487).