P-Rex and Vav Rac-GEFs in platelets control leukocyte recruitment to sites of inflammation

Abstract

Key Points• P-Rex and Vav Rac-GEFs cooperate in leukocyte recruitment during inflammation by facilitating leukocyte adhesion to the vascular endothelium.• P-Rex/Vav expression in platelets is required for vascular adhesion and recruitment of neutrophils and eosinophils into lung tissue.The small GTPase Rac is required for neutrophil recruitment during inflammation, but its guanine-nucleotide exchange factor (GEF) activators seem dispensable for this process, which led us to investigate the possibility of cooperation between Rac-GEF families. Thioglycollate-induced neutrophil recruitment into the peritoneum was more severely impaired in P-Rex1 2/2 Vav1 2/2 (P1V1) or P-Rex1 2/2 Vav3 2/2 (P1V3) mice than in P-Rex null or Vav null mice, suggesting cooperation between P-Rex and Vav Rac-GEFs in this process. Neutrophil transmigration and airway infiltration were all but lost in P1V1 and P1V3 mice during lipopolysaccharide (LPS)-induced pulmonary inflammation, with altered intercellular adhesion molecule 1-dependent slow neutrophil rolling and strongly reduced L-and E-selectin-dependent adhesion in airway postcapillary venules. Analysis of adhesion molecule expression, neutrophil adhesion, spreading, and migration suggested that these defects were only partially neutrophil-intrinsic and were not obviously involving vascular endothelial cells. Instead, P1V1 and P1V3 platelets recapitulated the impairment of LPS-induced intravascular neutrophil adhesion and recruitment, showing P-Rex and Vav expression in platelets to be crucial. Similarly, during ovalbumin-induced allergic inflammation, pulmonary recruitment of P1V1 and P1V3 eosinophils, monocytes, and lymphocytes was compromised in a plateletdependent manner, and airway inflammation was essentially abolished, resulting in improved airway responsiveness. Therefore, platelet P-Rex and Vav family Rac-GEFs play important proinflammatory roles in leukocyte recruitment. (Blood. 2015;125(7):1146-1158) IntroductionDuring inflammation, neutrophils are rapidly recruited from the bloodstream into inflamed tissues where they mount proinflammatory and antimicrobial responses.1 Recruitment occurs in a cascade of steps, beginning with the upregulation of P-selectin on the surface of endothelial cells that line postcapillary venules. P-selectin captures neutrophils from the bloodstream by engaging P-selectin glycoprotein ligand 1 (PSGL1) on their surface, enabling them to roll along the intraluminal wall. When captured, L-selectin on the neutrophil surface engages endothelial PSGL1 to support rolling, and endothelial E-selectin engages neutrophil PSGL1, among other counterligands, to slow rolling down. Binding of the neutrophil integrins LFA1 and Mac1 to their endothelial ligand intercellular adhesion molecule 1 (ICAM1) confers firm adhesion, and Mac1 enables the cells to crawl along the vessel wall before they actively transmigrate into the inflamed tissue by para-or transcellular routes.2 This recruitment cascade has largely been elucidated in the inflamed cremaster muscle and mesen...

Immunosuppression-Independent Role of Regulatory T Cells against Hypertension-Driven Renal Dysfunctions

“…Additional experiments have also revealed that the AngII-mediated stimulation of neutrophil migration and ROS production is Vav1 independent (Fabbiano, unpublished). These data are in agreement with previous results from the lab of H. Welch indicating no major defects in the in vivo biological properties of Vav1 Ϫ/Ϫ neutrophils (53,54). It would be important, in any case, to continue the analyses of Vav1 Ϫ/Ϫ T REG cells and neutrophils in order to assess whether this protein plays some catalysis-dependent or independent roles in any of these cell types.…”

Role of platelets in allergic airway inflammation

“…70 We have also demonstrated that the Rac-GEF proteins P-Rex and Vav, which are essential for leukocyte (neutrophil) motility, are also present in platelets and central to the signaling required for platelet-dependent leukocyte recruitment. 71 These observations open up the distinct possibility of targeting such signaling mechanisms as novel approaches for the development of anti-inflammatory drugs.…”

Rac‐GTPases and Rac‐GEFs in neutrophil adhesion, migration and recruitment

“…Although Vav GEFs alone are largely dispensable for neutrophil recruitment, they do cooperate with P‐Rex1 to regulate neutrophil adhesion, migration and tissue recruitment . Prex1 −/− Vav1 −/− neutrophils show reduced cell surface levels of LFA‐1 and Mac‐1 and have more profound defects in fMLP‐stimulated Rac1 and Rac2 activity, adhesion and migration than neutrophils which lack either the P‐Rex or Vav families . Similarly, neutrophil recruitment during sterile peritonitis is more severely impaired in Prex1 −/− Vav1 −/− or Prex1 −/− Vav3 −/− mice than in strains that lack either GEF family .…”