Cultured astrocytes express toll‐like receptors for bacterial products

TLDR

Astrocytes may contribute to inflammatory immune responses in the brain during microbial challenges, but the mechanisms of their activation remain unexplored. This study investigates the presence of Toll‑like receptors (TLRs) in primary murine astrocyte cultures. The authors isolated primary astrocytes and examined TLR mRNA expression, ligand‑induced up‑regulation, cytokine secretion, and protein localization via Western blot and immunofluorescence. Astrocytes constitutively express TLR2, TLR4, TLR5, and TLR9 mRNA, which is markedly up‑regulated by specific bacterial ligands, leading to IL‑6 production and confirming functional receptor expression. © 2003 Wiley‑Liss, Inc.

Abstract

Abstract It has become apparent that astrocytes may be important contributors to inflammatory immune responses within the brain in response to microbial challenges. To date, the mechanisms that underlie activation of this major glial cell type by such challenges have not been investigated. In the present study, we present evidence for members of a recently discovered family of receptors for highly conserved microbial components, the Toll‐like receptors (TLRs), in isolated cultures of primary murine astrocytes. We describe the low‐level constitutive expression of messenger RNA‐encoding TLR2, TLR4, TLR5, and TLR9 in resting cultures of these cells. Importantly, the level of expression of messenger RNA for each of these receptors is markedly elevated following exposure to specific bacteria‐derived ligands for these receptors. The functional expression of these receptor proteins is further supported by the ability of known ligands for each TLR to induce both message expression and protein secretion of the proinflammatory cytokine, interleukin‐6. In addition, the recent availability of antibodies to TLR2 and TLR4 has enabled us to demonstrate directly the presence of these receptors on astrocytes by Western blot and immunofluorescence analysis, respectively. Furthermore, we have confirmed the sensitivity of such receptor expression to ligand stimulation. The present demonstration of Toll‐like microbial pattern‐recognition receptors on primary astrocytes provides a mechanistic link between bacterial challenge and inflammatory immune responses that may be an important component of the pathologies of bacterially induced inflammatory CNS disorders. © 2003 Wiley‐Liss, Inc.