Regulation of Proinflammatory Cytokine Expression in Primary Mouse Astrocytes by Coronavirus Infection

Abstract

Previous studies have shown that proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-␣) and interleukin 6 (IL-6), are differentially induced in primary mouse astrocytes by mouse hepatitis virus strain A59 (MHV-A59) and MHV-2. However, the signaling events that trigger TNF-␣ and IL-6 induction in these cells upon MHV infection remain unknown. In this study, we explored the potential signaling events. We found that induction of TNF-␣ and IL-6 occurred as early as 2 h postinfection and was completely dependent on viral replication. Using inhibitors specific for three mitogen-activated protein kinases, we showed that induction of TNF-␣ and IL-6 by MHV-A59 infection was mediated through activation of the Janus N-terminal kinase signaling pathway, but not through the extracellular signal-regulated kinase or p38 signaling pathway. This finding was further confirmed with knockdown experiments using small interfering RNAs specific for Janus N-terminal kinase. Interestingly, while nuclear factor B (NF-B), a key transcription factor required for the expression of proinflammatory cytokines in most cell types, was activated in astrocytes during MHV-A59 infection, disruption of the NF-B pathway by peptide inhibitors did not significantly inhibit TNF-␣ and IL-6 expression. Furthermore, experiments using chimeric viruses demonstrated that the viral spike and nucleocapsid proteins, which play important roles in MHV pathogenicity in mice, are not responsible for the differential induction of the cytokines. These results illustrate the complexity of the regulatory mechanism by which MHV induces proinflammatory cytokines in primary astrocytes.

Coronavirus Infections in the Central Nervous System and Respiratory Tract Show Distinct Features in Hospitalized Children

“…Although high serum levels of IL-6, IL-8, and MCP-1 in SARS- and MERS-infected patients have been illustrated [17,18,19], we did not find a significant increase in the serum level of these cytokines among our patient cohort. However, we found that IL-6, IL-8, and MCP-1 were significantly accumulated in the cerebrospinal fluid of patients with CoV-CNS infection.…”

“…MCP-1 is a C-C chemokine that can initiate the transmigration of monocytes across the blood-brain barrier [16]. Several studies have shown that IL-6, IL-8, and MCP-1 contribute to severe respiratory disease progression in SARS infections [17,18,19]. Granulocyte colony-stimulating factor (G-CSF) expression is often induced during CoV infections, resulting in systemic (i.e., in the plasma) and local increases in inflammatory fluids either in mice or humans, such as patients with rheumatoid arthritis and severe respiratory syncytial virus infection [20,21,22].…”

Coronavirus-induced ER stress response and its involvement in regulation of coronavirus–host interactions

“…Finally, the MAP kinase JNK is known to regulate cytokine expression by directly activating the AP-1 via phosphorylation of c-Jun (Karin, 1995). In fact, it has been shown that the induction of pro-inflammatory cytokines TNF-␣ and IL-6 in primary mouse astrocytes infected with MHV-A59 is dependent on the activation of JNK, but not NF-B, ERK or p38 (Yu et al, 2009). Preliminary data from this group have also confirmed the important role of JNK and its upstream MAP kinase kinase 4/7 (MKK4/7) in the induction of IL-8 during IBV infection.…”

Regulation of Cellular MicroRNA Expression in Oligodendrocytes during Acute and Persistent Coronavirus Infection

“…While the number of miRNAs tested in the current experiments is rather limited, the results appear to suggest that miRNAs play a role in coronavirus replication. However, it is not known whether the net outcome of the altered miRNA expression contributes to restricting MHV replication as does the antiviral type I interferon response to MHV infection in N20.1 cells [32][33][34][35]. Nevertheless, our studies show that cellular miRNAs are potential regulators of viral replication and host gene expression during acute and persistent coronaviral infection that might contribute to the pathogenesis of coronavirus infection in oligodendrocytes in vitro and in vivo.…”

“…We have shown previously that 125 genes are up-regulated while 124 genes are downregulated in a mouse astrocytoma cell line infected by MHV in a genome-wide DNA microarray analysis [31]. Interestingly, many transcription factors such as extracellular regulatory kinase (Erk)-1/2, c-Jun, early growth regulator (Egr)-1, interferon regulatory factor (IRF)-3, nuclear factor (NF)-kB are activated in various types of cells by MHV infection [32][33][34][35]. As expression of many cellular genes is regulated by transcription factors, it is possible that expression of cellular miRNAs can be regulated by coronavirus infection through activation or suppression of the transcription factors.…”