CD14 release induced by P2X7 receptor restricts inflammation and increases survival during sepsis

Abstract

P2X7 receptor activation induces the release of different cellular proteins, such as CD14, a glycosylphosphatidylinositol (GPI)-anchored protein to the plasma membrane important for LPS signaling via TLR4. Circulating CD14 has been found at elevated levels in sepsis, but the exact mechanism of CD14 release in sepsis has not been established. Here we show for first time that P2X7 receptor induces the release of CD14 in extracellular vesicles, resulting in a net reduction in macrophage plasma membrane CD14 that functionally affects LPS, but not monophosphoryl lipid A, pro-inflammatory cytokine production. Also, we found that during a murine model of sepsis, P2X7 receptor activity is important for maintaining elevated levels of CD14 in biological fluids and a decrease in its activity results in higher bacterial load and exacerbated organ damage, ultimately leading to premature deaths. Our data reveal that P2X7 is a key receptor for helping to clear sepsis because it maintains elevated concentrations of circulating CD14 during infection.

Extracellular Vesicles: A Double-Edged Sword in Sepsis

“…Regarding research focusing on biological effects of EVs, most studies have been focusing on the effects of neutrophil-, monocyte/macrophage- and endothelial cell-derived EVs in sepsis. In this review, both pro- and anti-inflammatory effects are described for macrophage- [ 24 , 59 , 69 , 73 , 86 ] and neutrophil-derived EVs [ 74 , 79 ]. Moreover, neutrophil-derived EVs are described as anti-bacterial effectors [ 43 , 74 , 79 ] and monocyte-derived EVs are linked with TF-EV production and coagulation [ 39 , 49 , 110 ].…”

“…Another interesting finding is that LPS-stimulated macrophages can release CD14 via EV secretion upon P2X7 receptor stimulation, leading to decreased levels of membrane bound CD14 on macrophages, resulting in decreased IL-6, TNF and IL-1β production by these macrophages [ 86 ]. P2X7 receptor dependent release of CD14-containing EVs was found to play a role during sepsis because sepsis patients have elevated circulating CD14 plasma levels, while mice lacking P2X7 receptor signaling showed lowered serum levels of circulating CD14 and a decreased amount of CD14-EVs in peritoneal lavage fluid compared to wildtype mice [ 86 ]. Additionally, HSPA12B-containing EVs are reported to attenuate the production of pro-inflammatory mediators such as TNF and IL-1 by LPS-stimulated macrophages, via downregulation of NFκB activation [ 63 ].…”

“…There are also some studies focusing on the link between EVs from specific cellular sources and survival [ 42 , 46 , 50 , 86 , 117 ]. During the first days of sepsis, significantly increased levels of endothelial-derived EVs were detected in the blood of survivors compared to non-survivors [ 46 ].…”

“…Likewise, higher levels of leukocyte-derived EVs found during the first days in the blood and broncho-alveolar lavage fluid of sepsis patients suffering from acute respiratory stress syndrome were correlated with better patient survival [ 50 ]. Additionally, circulating CD14+ macrophage-derived EVs, released via P2X7 receptor activation, are linked with better survival in the CLP sepsis mouse model [ 86 ]. It was suggested that CD14 release by macrophages was mainly propagated by CD14-EV release and that this caused macrophage polarization to the anti-inflammatory phenotype due to the decreased CD14 presence in the macrophage membrane [ 86 ].…”

“…Additionally, circulating CD14+ macrophage-derived EVs, released via P2X7 receptor activation, are linked with better survival in the CLP sepsis mouse model [ 86 ]. It was suggested that CD14 release by macrophages was mainly propagated by CD14-EV release and that this caused macrophage polarization to the anti-inflammatory phenotype due to the decreased CD14 presence in the macrophage membrane [ 86 ]. As mentioned above, neutrophil-derived EVs carrying A2MG are elevated in a subset of sepsis patients and are shown to have anti-inflammatory and anti-bacterial effects [ 79 , 118 ].…”