The TLR3 ligand polyI:C downregulates connexin 43 expression and function in astrocytes by a mechanism involving the NF‐κB and PI3 kinase pathways

Abstract

Toll-like receptor 3 (TLR3) is a component of the innate immune response that responds to dsRNA viruses and virus replication intermediates. In this study we show that activation of astrocytes with the dsRNA mimetic polyinosinic-cytidylic acid (pI:C) results in loss of expression of connexin43 (Cx43) mRNA and protein while upregulating the expression of the ionotropic P2 receptor P2X(4)R. Analysis of the signaling pathways involved failed to demonstrate a role for the p38 MAP kinase, ERK, or JNK signaling pathways whereas an inhibitor of the PI3 kinase/Akt pathway effectively blocked the action of pI:C. Using adenoviral vectors containing a super-repressor of NF-kappaB (NF-kappaB SR) construct or a dominant negative interferon regulatory factor 3 (dnIRF3) construct showed that inhibition of both transcription factors also blocked the effects of pI:C. To explore the functional consequences of pI:C activation we used a pore-forming assay for P2X(4)R activity and a scrape loading assay for gap junction intercellular communication (GJIC). No pore-forming activity consistent with functional P2X(4)R expression was detected in either control or activated astrocytes. In contrast, robust Lucifer yellow transfer indicative of GJIC was detected in resting cells that was lost following pI:C activation. The dnIRF3 construct failed to restore GJIC whereas the NF-kappaB SR or the NF-kappaB inhibitor BAY11-7082 and the PI3K inhibitor LY294002 all significantly reversed the effect of pI:C on GJ connectivity. We conclude that activation of the innate immune response in astrocytes is associated with functional loss of GJIC through a pathway involving NF-kappaB and PI3 kinase.

Galectin-9 Protein Expression in Endothelial Cells Is Positively Regulated by Histone Deacetylase 3

“…38), one of which is the phosphorylation site at Ser-386. IRF3 Ser-386 phosphorylation is mediated by PI3K in response to virus infection (39). In our study, IFN-␥ induces IRF3 Ser-386 phosphorylation in a PI3K-and HDAC3-dependent manner.…”

Reciprocal Regulation between Proinflammatory Cytokine-induced Inducible NO Synthase (iNOS) and Connexin43 in Bladder Smooth Muscle Cells

“…Inhibition of NFB with SC514 completely abolished the increase in Cx43 expression. Several previous papers described the presence of an NFB-binding site in the promoter region of the Cx43 gene (39,40). However, the functional role of this site has not been firmly established.…”

Mechanisms of ATP‐ and glutamate‐mediated calcium signaling in white matter astrocytes

“…''Fast'' P2X 1 and P2X 3 receptor subtypes are activated and inactivated within milliseconds (North and Suprenant, 2000), and may not be involved in the relatively slow Ca 21 signals measured in this study. In comparison, P2X 2 and P2X 4 receptors, like P2X 7 receptors, are able to form pores that dilate in the sustained presence of ATP (Khakh et al, 1999), and have been demonstrated on astrocytes (Ashour and Deuchars, 2004;Kukley et al, 2001;Zhao et al, 2006 nerves indicates that the main action of glutamate is to trigger the release of ATP through pore-forming P2X 7 receptors. That some cells did respond directly to glutamate when P2 receptors were blocked and in the P2X 2=2 7 nerve suggests that a subpopulation of glia respond to glutamate directly.…”