TLR-Activated Gap Junction Channels Protect Mice against Bacterial Infection through Extracellular UDP Release.

Abstract

Extracellular UDP (eUDP), released as a danger signal by stressed or apoptotic cells, plays an important role in a series of physiological processes. Although the mechanism of eUDP release in apoptotic cells has been well defined, how the eUDP is released in innate immune responses remains unknown. In this study, we demonstrated that UDP was released in both Escherichia coli-infected mice and LPS- or Pam3CSK4-treated macrophages. Also, LPS-induced UDP release could be significantly blocked by selective TLR4 inhibitor Atractylenolide I and selective gap junction inhibitors carbenoxolone and flufenamic acid (FFA), suggesting the key role of TLR signaling and gap junction channels in this process. Meanwhile, eUDP protected mice from peritonitis by reducing invaded bacteria that could be rescued by MRS2578 (selective P2Y6 receptor inhibitor) and FFA. Then, connexin 43, as one of the gap junction proteins, was found to be clearly increased by LPS in a dose- and time-dependent manner. Furthermore, if we blocked LPS-induced ERK signaling by U0126, the expression of connexin 43 and UDP release was also inhibited dramatically. In addition, UDP-induced MCP-1 secretion was significantly reduced by MRS2578, FFA, and P2Y6 mutation. Accordingly, pretreating mice with U0126 and Gap26 increased invaded bacteria and aggravated mice death. Taken together, our study reveals an internal relationship between danger signals and TLR signaling in innate immune responses, which suggests a potential therapeutic significance of gap junction channel-mediated UDP release in infectious diseases.

• Authors: Juliang Qin, Guangxu Zhang, Xiaoyu Zhang, Binghe Tan, Zhangsheng Lv, Mingyao Liu, Hua Ren, Min Qian, Bing Du
• Journal: Journal of immunology (Baltimore, Md. : 1950) (J Immunol) Vol. 196 Issue 4 Pg. 1790-8 (Feb 15 2016) ISSN: 1550-6606 [Electronic] United States
• PMID: 26783339 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2016 by The American Association of Immunologists, Inc.

Chemical References

• Connexin 43
• GJA1 protein, mouse
• Tlr4 protein, mouse
• Toll-Like Receptor 4
• Toll-Like Receptors
• Uridine Diphosphate

Topics

• Animals
• Blotting, Western
• Connexin 43 (immunology, metabolism)
• Disease Models, Animal
• Enzyme-Linked Immunosorbent Assay
• Escherichia coli Infections (immunology)
• Female
• Gap Junctions (immunology)
• Immunity, Innate
• Macrophages, Peritoneal (immunology)
• Mice
• Mice, Inbred C57BL
• Real-Time Polymerase Chain Reaction
• Signal Transduction (immunology)
• Toll-Like Receptor 4 (immunology, metabolism)
• Toll-Like Receptors (immunology, metabolism)
• Uridine Diphosphate (immunology, metabolism)