Aim: To examine the neuroprotective effects of the Toll-like receptor 3 (TLR3) agonist Poly I:C in acute ischemic models in vitro and in vivo. Methods: Primary astrocyte cultures subjected to oxygen-glucose deprivation (OGD) were used as an in vitro simulated ischemic model. Poly I:C was administrated 2 h before OGD. Cell toxicity was measured using MTT assay and LDH leakage assay. The levels of TNFα, IL-6 and interferon-β (IFNβ) in the media were measured using ELISA. Toll/interleukin receptor domain-containing adaptor-inducing IFNβ (TRIF) protein levels were detected using Western blot analysis. A mouse middle cerebral artery occlusion (MCAO) model was u sed for in vivo study. The animals were administered Poly I:C (0.3 mg/kg, im) 2 h before MCAO, and examined with neurological deficit scoring and TTC staining. The levels of TNFα and IL-6 in ischemic brain were measured using ELISA. Results: Pretreatment with Poly I:C (10 and 20 μg/mL) markedly attenuated OGD-induced astrocyte injury, and significantly raised the cell viability and reduced the LDH leakage. Poly I:C significantly upregulated TRIF expression accompanied by increased downstream IFNβ production. Moreover, Poly I:C significantly suppressed the pro-inflammatory cytokines TNFα and IL-6 production. In mice subjected to MCAO, administration of Poly I:C significantly attenuated the neurological deficits, reduced infarction volume, and suppressed the increased levels of TNFα and IL-6 in the ischemic striatum and cortex. Conclusion: Poly I:C pretreatment exerts neuroprotective and anti-inflammatory effects in the simulated cerebral ischemia models, and the neuroprotection is at least in part due to the activation of the TLR3-TRIF pathway.

BackgroundCerebral ischemic preconditioning (IPC) protects brain against ischemic injury. Activation of Toll-like receptor 3 (TLR3) signaling can induce neuroprotective mediators, but whether astrocytic TLR3 signaling is involved in IPC-induced ischemic tolerance is not known.MethodsIPC was modeled in mice with three brief episodes of bilateral carotid occlusion. In vitro, IPC was modeled in astrocytes by 1-h oxygen-glucose deprivation (OGD). Injury and components of the TLR3 signaling pathway were measured after a subsequent protracted ischemic event. A neutralizing antibody against TLR3 was used to evaluate the role of TLR3 signaling in ischemic tolerance.ResultsIPC in vivo reduced brain damage from permanent middle cerebral artery occlusion in mice and increased expression of TLR3 in cortical astrocytes. IPC also reduced damage in isolated astrocytes after 12-h OGD. In astrocytes, IPC or 12-h OGD alone increased TLR3 expression, and 12-h OGD alone increased expression of phosphorylated NFκB (pNFκB). However, IPC or 12-h OGD alone did not alter the expression of Toll/interleukin receptor domain-containing adaptor-inducing IFNβ (TRIF) or phosphorylated interferon regulatory factor 3 (pIRF3). Exposure to IPC before OGD increased TRIF and pIRF3 expression but decreased pNFκB expression. Analysis of cytokines showed that 12-h OGD alone increased IFNβ and IL-6 secretion; 12-h OGD preceded by IPC further increased IFNβ secretion but decreased IL-6 secretion. Preconditioning with TLR3 ligand Poly I:C increased pIRF3 expression and protected astrocytes against ischemic injury; however, cells treated with a neutralizing antibody against TLR3 lacked the IPC- and Poly I:C-induced ischemic protection and augmentation of IFNβ.ConclusionsThe results suggest that IPC-induced ischemic tolerance is mediated by astrocytic TLR3 signaling. This reprogramming of TLR3 signaling by IPC in astrocytes may play an important role in suppression of the post-ischemic inflammatory response and thereby protect against ischemic damage. The mechanism may be via activation of the TLR3/TRIF/IRF3 signaling pathway.

BackgroundIt has been shown that chronic stress-induced depression is associated with exaggerated inflammatory response in the brain. Alpha7 nicotinic acetylcholine receptors (α7nAChRs) regulate the cholinergic anti-inflammatory pathway, but the role of cholinergic signaling and α7nAChR in chronic stress has not yet been examined.MethodsIn this study, we used a well-documented model of depression in which mice were exposed to 6 h of restraint stress for 21 consecutive days. Components of cholinergic signaling and TLR4 signaling were analyzed in the hippocampus. The main targets of neuroinflammation and neuronal damage were also evaluated after a series of tests for depression-like behavior.ResultsChronic restraint stress (CRS) induced alterations in components of central cholinergic signaling in hippocampus, including increases in choline acetyltransferase protein expression and decreases in nuclear STAT3 signaling. CRS also increased TLR4 signaling activity, interleukin-1β, and tumor necrosis factor-α expression, microglial activation, and neuronal morphologic changes. Cholinergic stimulation with the α7nAChR agonist DMXBA significantly alleviated CRS-induced depressive-like behavior, neuroinflammation, and neuronal damage, but these effects were abolished by the selective α7nAChR antagonist α-bungarotoxin. Furthermore, activation of α7nAChRs restored the central cholinergic signaling function, inhibited TLR4-mediated inflammatory signaling and microglial activity, and increased the number of regulatory T cells in the hippocampus.ConclusionsThese findings provide evidence that α7nAChR activation mitigates CRS-induced neuroinflammation and cell death, suggesting that α7nAChRs could be a new therapeutic target for the prevention and treatment of depression.Electronic supplementary materialThe online version of this article (10.1186/s12974-017-1007-2) contains supplementary material, which is available to authorized users.

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