Inhibition of tumor necrosis factor α-mediated NFκB activation and leukocyte adhesion, with enhanced endothelial apoptosis, by G protein-linked receptor (TP) ligands

Abstract

Tumor necrosis factor (TNF) α is a critical mediator of inflammation; however, TNFα is rarely released alone and the "cross-talk" between different classes of inflammatory mediators is largely unexplored. Thromboxane A2 (TXA2) is released during I/R injury and exerts its effects via a G protein-linked receptor (TP). In this study, we found that TXA2 mimetics stimulate leukocyte adhesion molecule (LAM) expression on endothelium via TPβ. The potential interaction between TXA2 and TNFα in altering endothelial survival and LAM expression was examined. IBOP, a TXA2 mimetic, attenuated TNFα-induced LAM expression in vitro, in a concentration-dependent manner, by preventing TNFα-enhanced gene expression, and also reduced TNFα-induced leukocyte adhesion to endothelium both in vitro and in vivo. IBOP abrogated TNFα-induced NFκB activation in endothelial cells, as determined by reduced IκB phosphorylation and NFκB nuclear translocation, by inhibiting the assembly of signaling intermediates with the intracellular domain of TNF receptors 1 and 2 in response to TNFα. This inhibition resulted from the Gαq-mediated enhancement of STAT1 activation and was reversed by anti-STAT1 antisense oligonucleotides. TNFα-mediated TNFR1-FADD association and caspase 8 activation were not inhibited by IBOP co-stimulation, however, resulting in a 2.6-fold increase in endothelial cell apoptosis. By stimulating the vessel wall and inducing endothelial cell apoptosis, TXA2, in combination with TNFα, may hamper the angiogenic response during inflammation or ischemia, thus reducing revascularization and tissue viability.