Toll-Like Receptors 2, -3 and -4 Prime Microglia but not Astrocytes Across Central Nervous System Regions for ATP-Dependent Interleukin-1β Release

Abstract

Interleukin-1β (IL-1β) is a crucial mediator in the pathogenesis of inflammatory diseases at the periphery and in the central nervous system (CNS). Produced as an unprocessed and inactive pro-form which accumulates intracellularly, release of the processed cytokine is strongly promoted by ATP acting at the purinergic P2X7 receptor (P2X7R) in cells primed with lipopolysaccharide (LPS), a Toll-like receptor (TLR) 4 ligand. Microglia are central to the inflammatory process and a major source of IL-1β when activated. Here we show that purified (>99%) microglia cultured from rat cortex, spinal cord and cerebellum respond robustly to ATP-dependent IL-1β release, upon priming with a number of TLR isoform ligands (zymosan and Pam3CSK4 for TLR2, poly(I:C) for TLR3). Cytokine release was prevented by a P2X7R antagonist and inhibitors of stress-activated protein kinases. Enriched astrocytes (≤5% microglia) from these CNS regions displayed responses qualitatively similar to microglia but became unresponsive upon eradication of residual microglia with the lysosomotropic agent Leu-Leu-OMe. Activation of multiple TLR isoforms in nervous system pathology, coupled with elevated extracellular ATP levels and subsequent P2X7R activation may represent an important route for microglia-derived IL-1β. This phenomenon may have important consequences for neuroinflammation and its position to the common pathology of CNS diseases.

Edaravone Attenuates the Proinflammatory Response in Amyloid-β-Treated Microglia by Inhibiting NLRP3 Inflammasome-Mediated IL-1β Secretion

“…Therefore, microglia were primed with 500 ng/ml LPS for 4 h and then exposed to different treatments. Consistent with the results from other studies [32,33], IL-1β was detected in culture supernatants from LPS-primed microglia. LPS-primed microglia were untreated or incubated with Aβ (1-10 μM) for 24 h. As shown in Fig.…”

The Neuroimmune Transcriptome and Alcohol Dependence: Potential for Targeted Therapies

“…Moreover, TLR4 expression and TLR2/4 association in cultured microglia appear to be necessary for alcohol-induced microglia activation and production of inflammatory mediators [38,57,60]. Facci et al (2014) demonstrated that TLR 2-4 endogenous ligands prime microglia (but not astrocytes) across the central nervous system for ATP-dependent IL-1β release [61]. Microglia-specific priming may be linked to the increased IL-1β that is observed in ethanol-fed mice and human alcoholic frontal cortex [38], providing evidence that microglia are necessary mediators of alcohol-induced inflammatory responses.…”

Lipopolysaccharide stimulation upregulated Toll-like receptor 4 expression in chicken cerebellum

“…Toll-like receptors (TLRs) belong to PRRs subfamily that largely expressed in many of the cells in CNS, especially in microglia. To date, 10 functional TLRs have been identified in humans (Kawai and Akira, 2010;Facci et al, 2014) and chicken (Kannaki et al, 2015) and as many as 13 in mouse (Reuven et al, 2014).…”