It is well established that mediators of peripheral inflammation are relayed to the brain and elicit sickness behavior via neuroinflammatory agents that target neuronal substrates. In the present study, we used double-stranded RNA (dsRNA), a viral replication intermediate, to mimic the acute phase of viral infection. C57BL/6 mice were injected intraperitoneally with 12 mg/kg of synthetic dsRNA, i.e., polyinosinic-polycytidylic acid (PIC). The treatment induced severe sickness behavior in the animals as revealed by the burrowing test performed 6 hr postinjection. PIC challenge also induced up-regulation of mRNA for several cytokines in the brain as determined by real-time quantitative RT-PCR. In all brain regions, i.e., the forebrain, brainstem, and cerebellum, the gene encoding the CXCL2 chemokine featured the most robust up-regulation over the basal level (saline-injected animals), followed by the genes encoding the CCL2 chemokine, interferon-beta (IFNbeta), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNFalpha), and interleukin-1beta (IL-1beta). The forebrain featured the highest extent of up-regulation of the Ifnb gene, whereas the other genes attained the highest expression in the cerebellum. Most of the genes featured transient up-regulation, with peaks occurring 3-6 hr after PIC challenge. The TNFalpha, CCL2, CXCL2, IFNbeta, and IL-1beta messages remained profoundly up-regulated even at 24 hr. The expression of genes encoding inducible and neuronal nitric oxide synthase (NOS) in the brain was not affected by the peripheral PIC challenge. However, the endothelial NOS message was initially down-regulated and subsequently up-regulated, indicating stimulation of cerebral vasculature.
Previously, we have shown that peripheral challenge of mice with double stranded RNA (dsRNA), a viral mimic, evokes global upregulation of cerebral inflammatory genes and, particularly, genes encoding chemokines. Because chemokine networks are potent modulators of brain function, the present study was undertaken to comprehensively characterize the cerebral response of chemokine ligand and receptor genes to peripheral immune system stimulation. Briefly, C57BL/6 mice were intraperitoneally injected with 12 mg/kg of polyinosinic-polycytidylic acid (PIC) and the expression of 39 mouse chemokine ligand and 20 receptor genes was monitored in the cerebellum by real time quantitative RT-PCR within 24 h. Almost half of the ligand genes featured either transient or sustained upregulation from several- to several thousand-fold. Five CXC type genes, i.e., Cxcl9, Cxcl11, Cxcl10, Cxcl2 and Cxcl1, were the most robustly upregulated, and were followed by six CC type genes, i.e., Ccl2, Ccl7, Ccl5, Ccl12, Ccl4 and Ccl11. Seven genes showed moderate upregulation, whereas the remaining genes were unresponsive. Six receptor genes, i.e., Cxcr2, Ccr7, Cxcr5, Ccr6, Ccr1 and Ccr5, featured a several-fold upregulation. Similar chemokine gene response was observed in the forebrain and brainstem. This upregulation of chemokine genes could be induced in naïve mice by transfer of blood plasma from PIC-challenged mice. Employing oligodeoxynucleotide-labeled PIC we further showed that intraperitoneally injected PIC was not transferred to the blood. In conclusion, peripheral PIC challenge elicits a broad upregulation of cerebral chemokine genes, and this upregulation is mediated by blood-borne agents.
Clinical evidence implicates peripheral inflammatory diseases as comorbid factors in epilepsy. The present study was designed to determine the effect of the acute phase of antiviral response on seizure susceptibility. Young adult mice were intraperitoneally injected with 12 mg/kg of a viral mimic, polyinosinic:polycytidylic acid (PIC). After 48 h, seizures were induced by subcutaneous injection of kainic acid (KA). PIC-pretreatment profoundly enhances vulnerability to excitotoxic insult as evidenced by increased seizure intensity and extended duration of status epilepticus. These results support the notion that peripheral viral infections may alter brain function resulting in enhanced predilection to seizures.
The family of Toll-like receptors (TLRs) expressed by innate immune cells recognizes a spectrum of microbial components as well as molecules released from injured tissues. TLR ligation activates intracellular signaling cascades that culminate in the up-regulation of proinflammatory genes. We have recently demonstrated that the up-regulation of inflammatory cytokines mediated by TLR4 in astrocytes is negatively controlled by the monomeric GTPases of Rho subfamily. The present study was undertaken to examine further the involvement of Rho proteins in the inflammatory response of astrocytes elicited by the ligation of three TLRs that use divergent signaling pathways. Astrocyte cultures established from newborn rat brains were challenged with ligands of TLR2, TLR3, and TLR4. The expression of genes encoding interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha (TNFalpha), interferon-beta (IFNbeta), and inducible nitric oxide synthase (NOS2) was up-regulated 24 hr after the challenge as determined by real-time RT-PCR. Pretreatment of the cells with toxin B, which specifically inactivates Rho proteins, enhanced the up-regulation of gene expression. The extent of this enhancement was both receptor and gene dependent. The enhancing effect of Rho protein inactivation was also evident at the protein level of IL-6 and NOS2 as revealed by ELISA and immunoblot analyses, respectively. These results suggest that Rho proteins control TLR-mediated up-regulation of inflammatory genes in astrocytes by interfering with multiple events along the signaling pathways.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.