Involvement of the P2X&lt;sub&gt;7&lt;/sub&gt; Purinergic Receptor and c-Jun N-Terminal and Extracellular Signal-Regulated Kinases in Cyclooxygenase-2 and Prostaglandin E&lt;sub&gt;2&lt;/sub&gt; Induction by LL-37

ATP is an important signaling molecule in the immune system, and it is able to bind the P2X7 purinergic receptor. Recently, our group showed that ATP-treated macrophages eliminate Leishmania amazonensis. It has been reported that leukotriene B4 (LTB4) reduces the parasitic load of infected macrophages. Additionally, it has been demonstrated that the P2X7 receptor can induce PLA2 activation and arachidonic acid mobilization. Based on these findings, we investigated whether LTB4 is produced upon P2X7 receptor activation and examined whether LTB4 modulates parasite elimination. Using macrophages lacking the P2X7 receptor, we observed that ATP was not able to reduce L. amazonensis load. This result suggests a role of the P2X7 purinergic receptor in parasite elimination. In addition, ATP was sufficient to induce LTB4 release from infected control macrophages but not from macrophages lacking the P2X7 receptor. Moreover, we found that ATP failed to decrease the parasitic load in 5-lipoxygenase (LO)–deficient macrophages. Treatment with the 5-LO inhibitor AA861 also impairs the ATP effect on parasitic loads. Furthermore, macrophages from 5-LO knockout mice eliminated L. amazonensis in the presence of exogenous LTB4, and macrophages obtained from P2X7 receptor knockout mice eliminated L. amazonensis when incubated with ionomycin. Finally, we demonstrated that in the presence of CP105696, an antagonist for LTB4 high-affinity receptor, ATP was not able to reduce parasitic load. These results indicate that P2X7 receptor activation leads to LTB4 formation, which is required for L. amazonensis elimination.

Section: Discussionmentioning

confidence: 99%

Leukotriene B4 Modulates P2X7 Receptor–MediatedLeishmania amazonensisElimination in Murine Macrophages

Chaves

Marques-da-Silva

Monteiro

et al. 2014

“…Our recent study also showed that LL-37 promotes LTB 4 and TXA 2 production via P2X 7 R (8). P2X 7 R is a ligand-gated ion channel, which is highly expressed by cells of the hematopoietic lineage, and it mediates cell death, killing of infectious organisms, and regulation of inflammatory responses (9). This receptor exists within the plasma membrane as a large multimolecular complex, consisting of b-actin, integrin b2, three heat shock proteins (10), and nonmuscle myosin (11).…”

mentioning

confidence: 99%

P2X7 Receptor Regulates Internalization of Antimicrobial Peptide LL-37 by Human Macrophages That Promotes Intracellular Pathogen Clearance

Tang

Basavarajappa

Haeggström

et al. 2015

Bioactive peptide LL-37/hCAP18, the only human member of the cathelicidin family, plays important roles in killing various pathogens, as well as in immune modulation. We demonstrate that LL-37 is internalized by human macrophages in a time-, dose-, temperature-, and peptide sequence–dependent endocytotic process. Both clathrin- and caveolae/lipid raft–mediated endocytosis pathways are involved in LL-37 internalization. We find that the P2X7 receptor (P2X7R) plays an important role in LL-37 internalization by human macrophages because significantly less internalized LL-37 was detected in macrophages pretreated with P2X7R antagonists or, more specifically, in differentiated THP-1 cells in which the P2X7R gene had been silenced. Furthermore, this P2X7R-mediated LL-37 internalization is primarily connected to the clathrin-mediated endocytosis pathway. In addition, our results demonstrate that internalized LL-37 traffics to endosomes and lysosomes and contributes to intracellular clearance of bacteria by human macrophages, coinciding with increased reactive oxygen species and lysosome formation. Finally, we show that human macrophages have the potential to import LL-37 released from activated human neutrophils. In conclusion, our study unveils a novel mechanism by which human macrophages internalize antimicrobial peptides to improve their intracellular pathogen clearance.

“…Interestingly, LL-37 has been shown by other groups to activate P2X7R directly in a manner not affected by apyrase (23, 39, 40). The differences in our results to those previously reported may stem from the different methodologies used in each study.…”

Section: Discussionmentioning

confidence: 91%

Human β Defensin-3 Increases CD86 Expression on Monocytes by Activating the ATP-Gated Channel P2X7

Lioi

Ferrari

Dubyak

et al. 2015

We previously showed that human beta defensin-3 (hBD-3), an epithelial cell derived antimicrobial peptide, mediates chemotaxis and activation of myeloid cells. Here, we provide evidence that hBD-3 induces the co-stimulatory molecule CD86 on primary human monocytes by a mechanism involving autocrine activation of ionotropic P2X7 receptors (P2X7R) by ATP. Incubation of monocytes with hBD-3 resulted in increased expression of both the CD80 and CD86 co-stimulatory molecules. Treatment of monocytes with a selective P2X7R antagonist inhibited the ability of hBD-3 to induce expression of CD86 but not CD80. The hBD-3-dependent upregulation of CD86 was also attenuated in monocytes incubated with apyrase, a potent scavenger of extracellular ATP. Finally, direct activation of monocyte P2X7 receptors by exogenous ATP mimicked the ability of hBD-3 to induce CD86 expression. These data suggest that hBD-3 induces monocyte activation by both P2X7-dependent (CD86 upregulation) and P2X7-independent (CD80 upregulation) signaling mechanisms and raise the possibility that activation of P2X7 receptors could play an important role in shaping the inflammatory microenvironment in conditions where hBD-3 is highly expressed, such as psoriasis or oral carcinoma.