TLR3‐mediated signal induces proinflammatory cytokine and chemokine gene expression in astrocytes: Differential signaling mechanisms of TLR3‐induced IP‐10 and IL‐8 gene expression

Abstract

Viral infection is one of the leading causes of brain encephalitis and meningitis. Recently, it was reported that Toll-like receptor-3 (TLR3) induces a double-stranded RNA (dsRNA)-mediated inflammatory signal in the cells of the innate immune system, and studies suggested that dsRNA may induce inflammation in the central nervous system (CNS) by activating the CNS-resident glial cells. To explore further the connection between dsRNA and inflammation in the CNS, we have studied the effects of dsRNA stimulation in astrocytes. Our results show that the injection of polyinosinic-polycytidylic acid (poly(I:C)), a synthetic dsRNA, into the striatum of the mouse brain induces the activation of astrocytes and the expression of TNF-alpha, IFN-beta, and IP-10. Stimulation with poly(I:C) also induces the expression of these proinflammatory genes in primary astrocytes and in CRT-MG, a human astrocyte cell line. Furthermore, our studies on the intracellular signaling pathways reveal that poly(I:C) stimulation activates IkappaB kinase (IKK), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) in CRT-MG. Pharmacological inhibitors of nuclear factor-kappaB (NF-kappaB), JNK, ERK, glycogen synthase kinase-3beta (GSK-3beta), and dsRNA-activated protein kinase (PKR) inhibit the expression of IL-8 and IP-10 in astrocytes, indicating that the activation of these signaling molecules is required for the TLR3-mediated chemokine gene induction. Interestingly, the inhibition of PI3 kinase suppressed the expression of IP-10, but upregulated the expression of IL-8, suggesting differential roles for PI3 kinase, depending on the target genes. These data suggest that the TLR3 expressed on astrocytes may initiate an inflammatory response upon viral infection in the CNS.

TLR3 Ligation Activates an Antiviral Response in Human Fetal Astrocytes: A Role for Viperin/cig5

“…They further showed that pIC induced a marked bias toward genes known for their role in host defense against viruses. As expected, and in agreement with previously published data (4,17), pIC also induced a wide array of chemokines and cytokines characteristic of TLR activation.…”

“…Using microarray technology, we found, in agreement with others (4,10,17), that pIC induced a wide range of cytokines and chemokines characteristic of an innate immune response, but we also noted a marked bias toward genes characterized for their role in antiviral responses when results were compared with similar data sets produced in response to the cytokine IL-1 (Table I). Cells were then stimulated with 10 g/ml pIC for 24 h, total cell homogenates were isolated and immunoblotted for viperin.…”

A destructive feedback loop mediated by CXCL10 in central nervous system inflammatory disease

“…It is important to note that previous in vivo studies of the inflammatory response to CNS virus infection and chronic EAE have demonstrated that astrocytes are a major source of CXCL10 13, 31, 32. Our observations of CXCL10 production by DCs and T cells in an antigen‐specific in vitro system do not rule out the possible additional production of CXCL10 by astrocytes or other cells in patients with PND.…”

Anti-inflammatory effects of 8-hydroxydeoxyguanosine in LPS-induced microglia activation: suppression of STAT3-mediated intercellular adhesion molecule-1 expression

“…The intrastriatal administration of drugs was modified from a previously described method (Heneka et al, 2000;Park et al, 2006). Briefly, male C57BL/6 mice (approx.…”

“…Brains were removed and postfixed at 4 o C overnight, transferred to 30% sucrose in PBS for 48 h, and then coronal sections (30 m thickness) were prepared on a cryostat. The immunohistochemical analysis of floating sections was performed as previously described (Park et al, 2006). Briefly, sections were incubated for 30 min with 3% H2O2 in 0.1 M PBS (pH 7.4), then blocked with a solution containing 5% normal goat/or horse serum, 2% BSA, 2% FBS, and 0.1% triton X-100 for 2 h at room temperature (RT).…”