Poly(I:C) promotes TNFa/TNFR1-dependent oligodendrocyte death in mixed glial cultures

Steelman, Andrew J; Li, Jianrong

In the current study we demonstrate that stimulation of mixed glial cultures with the viral mimic poly(I:C) causes preOL death in a non-cell autonomous fashion and through a TNFα/TNFR1-dependent mechanism. TNFα was derived exclusively from activated microglia as astrocytes neither secreted TNFα nor expressed intracellular TNFα following poly(I:C) stimulation. This was surprising as astrocytes clearly express TLR3 [7, 15, [32] [33] [34] , RIG-I [10, 35] and MDA-5 [11] and have been shown to produce TNFα in vivo [36] [37] [38] [39] . As these receptors are predominantly intracellular, a plausible explanation for these results could be the exogenous manner of the treatment. However, the fact that astrocytes up-regulated chemokines CCL2 and CCL5, but failed to induce TNFα indicates that exogenous poly(I: C) is capable of activating astrocytes thereby excluding the above possibility. In line with this finding, several recent studies have demonstrated that astrocytes stimulated with exogenous poly(I:C) dramatically increase cytokines IL-6, IFN-β, IL-8 and chemokine CCL2 and CCL5, but produce only negligible amounts of TNFα [11, 27] . Moreover, flow cytometric analysis by Zhou et al. convincingly demonstrates that while astrocytes express CCL2 following Pam3CSK4, poly(I:C) or LPS stimulation or LCMV infection, they do not express TNFα [40] . Together, these results strongly indicate either that, microglia are far superior at TNFα production when compared to astrocytes in vitro or that TNFα production in astrocyte cultures is attributable to residual microglia.