Toll-Like Receptor-Mediated Activation of CD39 Internalization in BMDCs Leads to Extracellular ATP Accumulation and Facilitates P2X7 Receptor Activation.

Ronglan Zhao,Deming Sun,Xiaoxiang Peng,Xumei Zhang,Jinjuan Qiao,Yansong Zhao,Xiangying Meng

doi:10.3389/fimmu.2019.02524

Ronglan Zhao, Deming Sun + Show 5 more

Open Access

https://doi.org/10.3389/fimmu.2019.02524

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Abstract

Toll-like receptors (TLRs) trigger innate immune responses through their recognition of conserved molecular ligands of either endogenous or microbial origin. Although activation, function, and signaling pathways of TLRs were already well-studied, their precise function in specific cell types, especially innate immune cells, needs to be further clarified. In this study, we showed that when significantly decreased amounts of membrane CD39, an adenosine triphosphate (ATP)-degrading enzyme, were detected in lipopolysaccharide (LPS)-treated bone marrow-derived dendritic cells (BMDCs), Cd39 mRNA expression, and whole-cell CD39 expression were at the same levels as those in untreated BMDCs. Further experiments demonstrated that the downregulation of membrane CD39 expression in LPS-treated BMDCs was mediated by endocytosis, leading to membrane-exposed CD39 downregulation, which was positively associated with decreased enzymatic activity in ATP metabolism and increased extracellular ATP accumulation. The accumulated ATP promoted intracellular calcium accumulation and IL-1β production in BMDCs through P2X7 signaling activation. Further research revealed that not only LPS but also other TLR ligands, excluding polyI:C, induced CD39 internalization in BMDCs and that the MyD88 pathway was critical in this process. The results suggested that the activation of CD39 internalization in DCs induced by a TLR ligand caused increased ATP accumulation, leading to P2X7 receptor activation that mediated a proinflammatory effect. Considering the strong modulatory effect of extracellular ATP accumulation on the immune response and inflammation, the manipulation of membrane CD39 expression on DCs may have implications on the regulation and treatment of inflammatory responses.

Highlights

Over the past two decades, increasing evidence has shown that tissue stress or damage is closely associated with an increased release of adenosine triphosphate (ATP) from the intracellular compartment into the extracellular compartment; this increased ATP release, in turn, exerts a strong modulatory effect on immune responses and inflammation [1,2,3,4,5,6,7,8]
The results revealed that Toll-like receptors (TLRs) ligand-induced CD39 internalization promotes the accumulation of extracellular ATP and the activation of P2X7 signaling in bone marrow-derived Dendritic cells (DCs) (BMDCs)
This finding indicated that processes in addition to transcriptional regulation must be involved in regulating the level of cell membrane-localized CD39 in LPS-treated BMDCs

Summary

Introduction

Over the past two decades, increasing evidence has shown that tissue stress or damage is closely associated with an increased release of adenosine triphosphate (ATP) from the intracellular compartment into the extracellular compartment; this increased ATP release, in turn, exerts a strong modulatory effect on immune responses and inflammation [1,2,3,4,5,6,7,8]. There are limited reports showing that P2X4 signaling regulates IL-1β production by bone marrow-derived DCs (BMDCs) [21]. Even this effect of P2X4 may be mediated by P2X7 [22]. We have reported that P2X7 signaling in DCs stimulates inflammation and accelerates experimental autoimmune uveitis [26]

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