Gαi2 is required for chemokine-induced neutrophil arrest

Abstract

Chemokines, including CXCL1, participate in neutrophil recruitment by triggering the activation of integrins, which leads to arrest from rolling. The downstream signaling pathways which lead to integrin activation and neutophil arrest following G-protein-coupled receptor engagement are incompletely understood. To test whether G␣ i2 is involved, mouse neutrophils in their native whole blood were investigated in mouse cremaster postcapillary venules and in flow chambers coated with P-selectin, ICAM-1, and CXCL1. Gnai2 Ϫ/Ϫ neutrophils showed significantly reduced CXCL1-induced arrest in vitro and in vivo. Similar results were obtained with leukotriene B 4 (LTB 4 ). Lethally irradiated mice reconstituted with Gnai2 Ϫ/Ϫ bone marrow showed a similar defect in chemoattractant-induced arrest as that of Gnai2 Ϫ/Ϫ mice. In thioglycollate-induced peritonitis and lipopolysaccaride (LPS)-induced lung inflammation, chimeric mice lacking G␣ i2 in hematopoietic cells showed about 50% reduced neutrophil recruitment similar to that seen in Gnai2 Ϫ/Ϫ mice. These data show that neutrophil G␣ i2 is necessary for chemokineinduced arrest, which is relevant for neutrophil recruitment to sites of acute inflammation.(Blood.

Defective Macrophage Migration in Gαi2- but Not Gαi3-Deficient Mice

“…Moreover, increased blood monocyte numbers were noted in Ga i2 -deficient mice, whereas monocytes in the bone marrow (BM) are not affected (Ref. 22; data not shown). To determine the potential role of the individual Ga i proteins in the homing of monocytes and/or macrophages, we first examined whether the presence of Ga i2 and Ga i3 is needed for proper distribution of macrophages at different organ sites.…”

“…Previously, it was shown that lack of Ga i2 leads to defects in the trafficking of T and B cells to lymph nodes (18,19) and in the recruitment of eosinophils and neutrophils to sites of inflammation (20,22,23). Moreover, increased blood monocyte numbers were noted in Ga i2 -deficient mice, whereas monocytes in the bone marrow (BM) are not affected (Ref.…”

“…Moreover, GPCR-induced activation of platelets is affected in Ga i2 2/2 mice (21). Ga i2 has also been reported to regulate the migration of neutrophils in acute inflammation (20,22). In the lung Arthus reaction, capillary leakage and neutrophil influx are reduced in the absence of the Ga i -coupled C5a receptor (C5aR) as well as Ga i2 but not Ga i3 (23).…”

Reactive Oxygen Species in Inflammation and Tissue Injury

“…In contrast to selectin-mediated adhesion, which leads to the rolling of neutrophils, adhesion of leukocytes by b 2 integrins is firm and is regarded an essential step for transendothelial migration of inflammatory cells. b 2 -integrins are activated by chemokines such as CXCL1 (stored in small cytoplasmic granules) and CXCL8 (stored in Weibel-Palade bodies), which are secreted by endothelial cells (456,465). The binding of chemokines to chemokine receptors (CXCR1 and CXCR2) changes the conformation of integrins from bent to fully extended high-affinity configuration, enabling neutrophil arrest by binding to ICAM-1 that is expressed in endothelial cells (Fig.…”

“…The binding of chemokines to chemokine receptors (CXCR1 and CXCR2) changes the conformation of integrins from bent to fully extended high-affinity configuration, enabling neutrophil arrest by binding to ICAM-1 that is expressed in endothelial cells (Fig. 7b) (465). b 2 integrins are grouped into the categories according to the b subunit they contain.…”