Platelet secretion of CXCL4 is Rac1‐dependent and regulates neutrophil infiltration and tissue damage in septic lung damage

Abstract

BACKGROUND AND PURPOSEPlatelets are potent regulators of neutrophil accumulation in septic lung damage. We hypothesized that platelet-derived CXCL4 might support pulmonary neutrophilia in a murine model of abdominal sepsis. EXPERIMENTAL APPROACHPolymicrobial sepsis was triggered by coecal ligation and puncture (CLP) in C57BL/6 mice. Platelet secretion of CXCL4 was studied by using confocal microscopy. Plasma and lung levels of CXCL4, CXCL1 and CXCL2 were determined by ELISA. Flow cytometry was used to examine surface expression of Mac-1 on neutrophils. KEY RESULTSCLP increased CXCL4 levels in plasma, and platelet depletion reduced plasma levels of CXCL4 in septic animals. Rac1 inhibitor NSC23766 decreased the CLP-enhanced CXCL4 in plasma by 77%. NSC23766 also abolished PAR4 agonist-induced secretion of CXCL4 from isolated platelets. Inhibition of CXCL4 reduced CLP-evoked neutrophil recruitment, oedema formation and tissue damage in the lung. However, immunoneutralization of CXCL4 had no effect on CLP-induced expression of Mac-1 on neutrophils. Targeting CXCL4 attenuated plasma and lung levels of CXCL1 and CXCL2 in septic mice. CXCL4 had no effect on neutrophil chemotaxis in vitro, indicating it has an indirect effect on pulmonary neutrophilia. Intratracheal CXCL4 enhanced infiltration of neutrophils and formation of CXCL2 in the lung. CXCR2 antagonist SB225002 markedly reduced CXCL4-provoked neutrophil accumulation in the lung. CXCL4 caused secretion of CXCL2 from isolated alveolar macrophages. CONCLUSIONS AND IMPLICATIONSRac1 controls platelet secretion of CXCL4 and CXCL4 is a potent stimulator of neutrophil accumulation in septic lungs via generation of CXCL2 in alveolar macrophages. Platelet-derived CXCL4 plays an important role in lung inflammation and tissue damage in polymicrobial sepsis.

Measuring and interpreting platelet-leukocyte aggregates

“…These studies indicate that, depending on the underlying pathology, PNAs are not always mediated by classic P-selectin/PSGL-1 binding, but rather by other receptor-ligand interactions or via soluble mediators. Indeed, in LPS-induced ALI platelet-derived CXCL4 and CCL5 control neutrophil infiltration via induction of CXCL2-release by alveolar macrophages (126,127). Furthermore, sequestrated platelets in the pulmonary microcirculation of TRALI-induced mice promote NET formation (128).…”

Platelet Interaction with Innate Immune Cells

“…Platelet inhibition reduces platelet-monocyte interaction and plasma levels of TNF-α during LPS-induced endotoxaemia in humans [67] and mice [68]. Platelet-derived CXCL4 and CCL5 are critical mediators of septic lung damage secondary to polymicrobial sepsis in a caecal ligation puncture (CLP) model as they trigger CXCL2 release of resident alveolar macrophages, thereby promoting neutrophil infiltration and tissue damage [69,70].…”

Feedback Amplification of Neutrophil Function

“…Activated platelets also release CXCL4 and CCL5 from their α-granules that promote neutrophil accumulation in septic lungs in the coecal ligation and puncture model through the release of CXCL2 from alveolar macrophages [95,96]. On the other hand, neutrophil-derived cathepsin G can trigger platelet activation through the protease-activated receptor 4 (PAR4) and mediate intracellular calcium signaling [97].…”