Activation of vascular endothelial growth factor receptor-3 in macrophages restrains TLR4-NF-κB signaling and protects against endotoxin shock.

ABSTRACT

Toll-like receptors (TLRs) are critical in mediating innate immune responses against infections. However, uncontrolled TLR-triggered inflammation is associated with endotoxin shock. To better understand the homeostatic mechanisms induced by TLR4 signaling, we screened a group of key cytokines, chemokines, growth factors, and their receptors for bacteria- or LPS-induced expression. The surface vascular endothelial growth factor receptor-3 (VEGFR-3) and its ligand VEGF-C were upregulated in macrophages. VEGFR-3 ligation by VEGF-C significantly attenuated proinflammatory cytokine production. Notably, ablation of the ligand-binding domain or tyrosine kinase activity of VEGFR-3 rendered mice more sensitive to septic shock. VEGFR-3 restrained TLR4-NF-κB activation by regulating the PI3-kinase-Akt signaling pathway and SOCS1 expression. Aside from targeting lymphatic vessels, we suggest a key role of VEGFR-3 on macrophages to prevent infections that is complicated with lymphoedema. Thus, VEGFR-3-VEGF-C signaling represents a "self-control" mechanism during antibacterial innate immunity.