Ligand-Activated Peroxisome Proliferator-Activated Receptor δ Attenuates Vascular Oxidative Stress by Inhibiting Thrombospondin-1 Expression

Abstract

Thrombospondin-1 (TSP-1) is implicated in vascular diseases associated with oxidative stress, such as abdominal aortic aneurysms, ischemia-reperfusion injury, and atherosclerosis. However, the regulatory mechanisms underlying TSP-1 expression are not fully elucidated. In this study, we found that peroxisome proliferator-activated receptor δ (PPARδ) inhibited oxidative stress-induced TSP-1 expression and migration in vascular smooth muscle cells (VSMCs). Activation of PPARδ by GW501516, a specific ligand for PPARδ, significantly attenuated hydrogen peroxide (H₂O₂)-induced expression of TSP-1 in VSMCs. Small interfering RNA-mediated knockdown of PPARδ and treatment with GSK0660, a selective PPARδ antagonist, reversed the effect of GW501516 on H₂O₂-induced expression of TSP-1, suggesting that PPARδ is associated with GW501516 activity. Furthermore, JNK (c-Jun N-terminal kinase), but not p38 and ERK (extracellular signal-regulated kinase), mediated PPARδ-dependent inhibition of TSP-1 expression in VSMCs exposed to H₂O₂. GW501516- activated PPARδ also reduced the H₂O₂-induced generation of reactive oxygen species, concomitant with inhibition of VSMC migration. In particular, TSP-1 contributed to the action of PPARδ in the regulation of H₂O₂-induced interleukin-1β expression. These results suggest that PPARδ-modulated downregulation of TSP-1 is associated with reduced cellular oxidative stress, thereby inhibiting H₂O₂-induced pheno­typic changes in vascular cells.