Rac1-dependent secretion of platelet-derived CCL5 regulates neutrophil recruitment via activation of alveolar macrophages in septic lung injury

Abstract

Accumulating evidence suggest that platelets play an important role in regulating neutrophil recruitment in septic lung injury. Herein, we hypothesized that platelet-derived CCL5 might facilitate sepsis-induced neutrophil accumulation in the lung. Abdominal sepsis was induced by CLP in C57BL/6 mice. CLP increased plasma levels of CCL5. Platelet depletion and treatment with the Rac1 inhibitor NSC23766 markedly reduced CCL5 in the plasma of septic mice. Moreover, Rac1 inhibition completely inhibited proteasePAR4-induced secretion of CCL5 in isolated platelets. Immunoneutralization of CCL5 decreased CLP-induced neutrophil infiltration, edema formation, and tissue injury in the lung. However, inhibition of CCL5 function had no effect on CLP-induced expression of Mac-1 on neutrophils. The blocking of CCL5 decreased plasma and lung levels of CXCL1 and CXCL2 in septic animals. CCL5 had no effect on neutrophil chemotaxis in vitro, suggesting an indirect effect of CCL5 on neutrophil recruitment. Intratracheal challenge with CCL5 increased accumulation of neutrophils and formation of CXCL2 in the lung. Administration of the CXCR2 antagonist SB225002 abolished CCL5-induced pulmonary recruitment of neutrophils. Isolated alveolar macrophages expressed significant levels of the CCL5 receptors CCR1 and CCR5. In addition, CCL5 triggered significant secretion of CXCL2 from isolated alveolar macrophages. Notably, intratracheal administration of clodronate not only depleted mice of alveolar macrophages but also abolished CCL5-induced formation of CXCL2 in the lung. Taken together, our findings suggest that Rac1 regulates platelet secretion of CCL5 and that CCL5 is a potent inducer of neutrophil recruitment in septic lung injury via formation of CXCL2 in alveolar macrophages.

CXCR1-mediated neutrophil degranulation and fungal killing promote Candida clearance and host survival

“…S14), we reasoned that Cxcr2 may drive renal neutrophil recruitment during infection in the absence of Cxcr1. To test this, we treated Cxcr1 −/− mice with vehicle or the selective Cxcr2 antagonist SB225002, which has been successfully used to inhibit Cxcr2-dependent neutrophil trafficking in mouse models of infection and inflammation in vivo (20,21). We found that Cxcr2 inhibition did not impair neutrophil accumulation in Candida -infected kidneys of Cxcr1 −/− mice (Fig.…”

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).…”

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].…”