Toll-like receptor 2-blocking antibodies promote angiogenesis and induce ERK1/2 and AKT signaling via CXCR4 in endothelial cells.

ABSTRACT

OBJECTIVE: Toll-like receptor 2 (TLR2) inhibition by function blocking antibodies (ABs) is associated with enhanced preservation of endothelial cell function during vascular disease. In the present study, we investigated the capacity of TLR2-blocking ABs to modulate the angiogenic response of endothelial cells in vitro and in vivo. APPROACH AND RESULTS: Incubation of endothelial cells with mono- or polyclonal anti-TLR2 ABs resulted in increased tube formation, sprouting, and migration of endothelial cells compared with controls. In a mouse model of hindlimb ischemia, using TLR2-deficient or anti-TLR2 AB-treated wild-type mice resulted in increased new capillary formation and enhanced reperfusion. The effects of anti-TLR2 ABs were similar to those exerted by stromal cell-derived factor-1, and we show that anti-TLR2 ABs yet not TLR2 ligands lead to comparable activation of extracellular signal-regulated kinase1/2 and AKT but not p38 mitogen-activated protein kinase as activation of the CXCR4 canonical signal transduction pathways by stromal cell-derived factor-1. Immunoprecipitation of TLR2 revealed that anti-TLR2 ABs initiate an association of TLR2 with CXCR4 and mitogen-activated protein kinase activation. The proangiogenic properties of anti-TLR2 ABs were abolished by both G-protein inhibition and CXCR4 knockdown in endothelial cells. CONCLUSIONS: Our results provide evidence for a proangiogenic effect of TLR2-blocking ABs on endothelial cells in vitro and in vivo. They identify a novel molecular mechanism linking TLR2 to angiogenic processes that is independent from the activation of inflammatory cascades and further support the concept of a beneficial effect of TLR2 inhibition for endothelial cell function in vascular disease.