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.

mTOR- and SGK-Mediated Connexin 43 Expression Participates in Lipopolysaccharide-Stimulated Macrophage Migration through the iNOS/Src/FAK Axis

“…Recently, Qin et al (20) found that Cx43 is the most abundant connexin in RAW 264.7 cells and that its expression is increased by LPS, consistent with our findings. Additionally, growing evidence has indicated that connexins are involved in inflammatory signaling, such as adhesion molecule expression and leukocyte transmigration (21,22).…”

“…In contrast, GSK650349 and Torin2 inhibited the upstream components of the mTOR/SGK/Cx43 signaling pathway, thereby suppressing the movement of a broad range of myeloid cells. Additionally, inhibition of macrophage recruitment by blocking the hemichannel may partly contribute to weakened bacteria clearance because Cx43-mediated UDP release may be involved in mediating the effects of Gap19 treatment (20). Furthermore, mice survival in the acute peritonitis mouse model was depressed by Gap19, which further confirmed the pivotal role of Cx43 hemichannel in the fight against bacterial infection.…”

Connexin-43 dependent ATP release mediates macrophage activation during peritonitis

“…Our data has shown that ATP released from peritoneal macrophages is an active process that occurs in response to TLR-2 and TLR-4 agonists in a CX43dependent manner. Increased expression of CX43 on macrophages following TLR-4 pathway activation has been previously shown (22). Our study has extended this observation by showing the functional role of CX43 for autocrine signaling in macrophages.…”

Virus-Triggered ATP Release Limits Viral Replication through Facilitating IFN-β Production in a P2X7-Dependent Manner

“…***p , 0.001. eliminate the potential damage from pathogens. Previous studies have shown that nucleotides, such as ATP, UTP, and UDP, could be released through multiple plasma membrane channels during different stages of infection (8,21). Moreover, the spatial and temporal release pattern of endogenous danger signals suggests different roles in the fight against invading pathogens.…”