Abstract
The cell type that normally limits the inflammatory and atherosclerotic process is the vascular endothelial cell (EC) that can be regulated by proinflammatory and various stresses. Toll-like receptor-4 (TLR4) plays an important role in the pathogenesis of atherosclerosis, in part, by activating apoptosis signal-regulating kinase 1 (ASK1) to initiate the activation of MAP kinases pathways and the expression of inflammatory genes. In the present study, we test the hypothesis that AGI-1067 acts as an anti-inflammatory agent by inhibiting the activation of ASK1 in human EC. Pretreatment of human aortic endothelial cells with AGI-1067 inhibits TLR4 ligand (LPS)-induced activation of ASK1 and the downstream p38 and c-Jun N-terminal kinase (JNK) MAP kinases. LPS dissociates two endogenous inhibitors thioredoxin-1 (Trx1) and 14-3-3 from ASK1, leading to ASK1 autoactivation. Interestingly, AGI-1067 inhibits the dissociation of Trx1, but not 14-3-3, from ASK1. However, inhibition of Trx1 dissociation from ASK1 by AGI-1067 is sufficient to suppress LPS-mediated phosphorylation of the transcription factors c-Jun and activating transcription factor 2, and inhibit LPS-induced inflammatory genes including vascular cell adhesion molecule 1, E-selectin, IL-6 and monocyte chemoattractant protein 1. Our findings suggest that AGI-1067 as a unique ASK1 inhibitor to inhibit TLR4-mediated ASK1 activation, contributing to its anti-inflammatory properties.