Gab2 (Grb2-Associated Binder2) Plays a Crucial Role in Inflammatory Signaling and Endothelial Dysfunction

Abstract

Objective: In response to inflammatory insult, endothelial cells express cell adhesion molecules and TF (tissue factor), leading to increased adhesion of leukocytes to the endothelium and activation of coagulation. Enhanced coagulation could further exacerbate inflammation. Identifying key signaling molecule(s) that drive both inflammation and coagulation may help devise effective therapeutic strategies to treat inflammatory and thrombotic disorders. The aim of the current study is to determine the role of Gab2 (Grb2-associated binder2), which is known to play a crucial role in the signaling evoked by growth factors and antigen receptors, in inflammatory signaling pathways and its contribution to vascular dysfunction. Approach and Results: WT (wild type) and Gab2-silenced endothelial cells were treated with TNFα (tumor necrosis factor alpha), IL (interleukin)-1β, or lipopolysaccharide (LPS). Activation of key signaling proteins in the inflammatory signaling pathways and expression of cell adhesion molecules, TF, and inflammatory cytokines were analyzed. Gab2-/- and WT littermate mice were challenged with LPS or S pneumoniae (Streptococcus pneumoniae), and parameters of inflammation and activation of coagulation were assessed. Gab2 silencing in endothelial cells markedly attenuated TNFα-induced, IL-1β-induced, and LPS-induced expression of TF, cell adhesion molecules, and inflammatory cytokines/chemokines. Gab2 silencing suppressed TNFα-induced, IL-1β-induced, and LPS-induced phosphorylation and ubiquitination of TAK1 (transforming growth factor beta-activated kinase 1) and activation of MAPKs (mitogen-activated protein kinases) and NF-κB (nuclear factor kappa B). Immunoprecipitation studies revealed that the Src kinase Fyn phosphorylates Gab2. Gab2-/- mice are protected from LPS or S pneumoniae-induced vascular permeability, neutrophil infiltration, thrombin generation, NET formation, cytokine production, and lung injury. Conclusions: Our studies identify, for the first time, that Gab2 integrates signaling from multiple inflammatory receptors and regulates vascular inflammation and thrombosis.