ATP‐gated P2X1 ion channels protect against endotoxemia by dampening neutrophil activation

Abstract

Summary. Background: In sepsis, extracellular ATP, secreted by activated platelets and leukocytes, may contribute to the crosstalk between hemostasis and inflammation. Previously, we showed that, in addition to their role in platelet activation, ATP‐gated P2X1 ion channels are involved in promoting neutrophil chemotaxis. Objectives: To elucidate the contribution of P2X1 ion channels to sepsis and the associated disturbance of hemostasis. Methods: We used P2X1−/− mice in a model of lipopolysaccharide (LPS)‐induced sepsis. Hemostasis and inflammation parameters were analyzed together with outcome. Mechanisms were further studied ex vivo with mouse and human blood or isolated neutrophils and monocytes. Results: P2X1−/− mice were more susceptible to LPS‐induced shock than wild‐type mice, despite normal cytokine production. Plasma levels of thrombin–antithrombin complexes were higher, thrombocytopenia was worsened, and whole blood coagulation time was markedly reduced, pointing to aggravated hemostasis disturbance in the absence of P2X1. However, whole blood platelet aggregation occurred normally, and P2X1−/− macrophages displayed normal levels of total tissue factor activity. We found that P2X1−/− neutrophils produced higher amounts of reactive oxygen species. Increased amounts of myeloperoxidase were released in the blood of LPS‐treated P2X1−/− mice, and circulating neutrophils and monocytes expressed higher levels of CD11b. Neutrophil accumulation in the lungs was also significantly augmented, as was lipid peroxidation in the liver. Desensitization of P2X1 ion channels led to increased activation of human neutrophils and enhanced formation of platelet–leukocyte aggregates. Conclusions: P2X1 ion channels play a protective role in endotoxemia by negatively regulating systemic neutrophil activation, thereby limiting the oxidative response, coagulation, and organ damage.

P2X1 expressed on polymorphonuclear neutrophils and platelets is required for thrombosis in mice

“…Specific pathogen-free homozygous P2X1 2/2 have been described previously. 12,13 All animal care and experimental procedures were performed as recommended by the European Community Guidelines (directive 2010/63/ UE) and approved by the Marseille Ethical Committee #14 ( protocol number: 27-28092012).…”

The P2X1 Receptor Is Required for Neutrophil Extravasation during Lipopolysaccharide-Induced Lethal Endotoxemia in Mice

“…These two mechanisms are not mutually exclusive, and both might contribute to the exacerbation of tissue injury and increased lethality. Others investigators reported that P2X 1 receptor deficiency failed to protect against, and rather slightly increased, mortality in LPS-induced endotoxemia (49). The reasons for these discrepancies are not clear.…”

Impaired P2X1 Receptor–Mediated Adhesion in Eosinophils from Asthmatic Patients

“…Although P2X1 currents are also relatively small in these cells (,100 pA/pF) (46,54), their physiological effects can be rather extensive. For example, P2X1 receptors promote neutrophil chemotaxis (46) and protect against endotoxemia by dampening neutrophil activation (35). In platelets, P2X1 amplifies the responses (e.g., aggregation and dense granule secretion) of many ligands (e.g., collagen, thrombin, and ADP) (55,56).…”

“…P2X1 receptor regulates integrin activity in hematic cells, such as platelets (54), neutrophils, and monocytes (35), whereas in healthy eosinophils, P2X1 activation upregulates CD11b expression (23). The integrin a M b 2 is involved in eosinophil adherence-dependent function, including transmigration and degranulation (32,37,57).…”

“…P2X1 receptor regulates CD11b (from the integrin complex a M b 2 ) expression in many hematic cell types (23,35,36). a,b-meATP (10 mM) caused an increase in CD11b activated form (37) on eosinophils from healthy donors (143 6 21% of control response, donors n = 13, p = 0.0409) but not from asthmatic donors (108 6 11% of control response, n = 10) (Fig.…”