CD39 limits P2X7 receptor inflammatory signaling and attenuates sepsis-induced liver injury

Abstract

Background & Aims The severity of sepsis can be linked to excessive inflammatory responses resulting in hepatic injury. P2X7 receptor activation by extracellular ATP (eATP) exacerbates inflammation by augmenting cytokine production; while CD39 (ENTPD1) scavenges eATP to generate adenosine, thereby limiting P2X7 activation and resulting in A2A receptor stimulation. We aim to determine the functional interaction of P2X7 and A2A receptors on controlling macrophage response, consequently impacting the outcome of sepsis and liver injury. Methods Sepsis was induced by cecal ligation and puncture in C57BL/6 wild-type (WT) and CD39−/− mice. Several in vitro assays were performed using peritoneal or bone marrow derived macrophages to determine CD39 ectonucleotidase activity and its role in sepsis-induced liver injury. Results CD39 expression in macrophages limits ATP-P2X7 receptor pro-inflammatory signaling. P2X7 receptor paradoxically boosts CD39 activity. Inhibition and/or deletion of P2X7 receptor in LPS-primed macrophages attenuates cytokine production and inflammatory signaling as well as preventing ATP-induced increases in CD39 activity. Septic CD39−/− mice exhibit higher levels of inflammatory cytokines and show more pronounced liver injury than WT mice. Pharmacological P2X7 blockade largely prevents tissue damage, cell apoptosis, cytokine production, and the activation of inflammatory signaling pathways in the liver from septic WT, while only attenuating these outcomes in CD39−/− mice. Furthermore, the combination of P2X7 blockade with adenosine A2A receptor stimulation completely inhibits cytokine production, the activation of inflammatory signaling pathways, and protects septic CD39−/− mice against liver injury. Conclusions CD39 attenuates sepsis-associated liver injury by scavenging eATP and ultimately generating adenosine. We propose boosting of CD39 would suppress P2X7 responses and trigger adenosinergic signaling to limit systemic inflammation and restore liver homeostasis during the acute phase of sepsis.

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“…( 30 , 36 , 62 ). In the innate immunity, activation of P2Y 2 and P2X7 receptors leads to stimulation of myeloid cells and promotes chemotaxis of macrophages and neutrophils ( 38 , 63 – 65 ). At the same time, engagement of P2Y 2 and P2X7 receptors induces dendritic cells (DCs) activation and chemotaxis ( 66 ).…”

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“…The liver is the key organ that maintains host homeostasis and plays an important role in host‐defense activities; hence, it is one of the most important “target” organs upon microbiota infection during sepsis. Unfortunately, sepsis‐induced liver dysfunction is associated with poor clinical outcomes . Few therapeutic approaches are currently available to reduce the burden of this life‐threatening complication.…”

“…Unfortunately, sepsis-induced liver dysfunction is associated with poor clinical outcomes. (8,9) Few therapeutic approaches are currently available to reduce the burden of this life-threatening complication. Thus, investigating the pathogenesis of sepsis-induced organ injury, including liver dysfunction, is important to develop more-effective prevention and treatment strategies.…”

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“…Combined P2×7 blockade and A2A receptor activation is required to protect septic CD39-deficient mice against inflammation-induced tissue injury. 63 Extracellular release of ATP by dead or dying cells also serves as a 'find-me' signal promoting chemotaxis of monocytes, macrophages and neutrophils. 15 64 Notably, ATP is released in a polarized fashion by macrophages, resulting in the accumulation of extracellular ATP near the cell surface closest to the source of chemotactic stimuli in order to amplify chemotactic signals by activating P2Y2…”