Abstract 8403: High Mobility Group Box-1 Stimulates Vascular Smooth Muscle Cells Migration via TLR4-dependent PI3K/Akt Pathway Activation

Abstract

Background: Migration of vascular smooth muscle cells (VSMCs) is a key event in neointimal formation and atherosclerosis. High mobility group box-1 (HMGB1), a highly conserved nuclear protein, can also act as an extracellular chemotactic cytokine for VSMCs. However, the role of HMGB1 receptors and details of signaling in VSMCs migration are largely unexplored. Toll-like receptor 4 (TLR4), a member of HMGB1 cell-surface receptors, is widely distributed in the vasculature. Moreover, TLR4 and its downstream PI3K/Akt pathway have been reported to regulate cell differentiation, proliferation and migration. Therefore, we determined whether TLR4 signaling and PI3K/Akt pathway activation occur in HMGB1-induced VSMCs migration. Methods and results: VSMCs from rat thoracic aorta were studied. We found that HMGB1 stimulated VSMCs migration in a dose-dependent manner, with the highest value (about 3.5-fold increase). In addition, incubation of VSMCs with HMGB1 (100 ng/ml) caused a rapid increase in PI3K activity and Akt phosphorylation ( P both<0.05). Silencing of TLR4 with siRNA significantly inhibited the HMGB1-induced migration of VSMCs by 49.7±6.3%, in comparison to Control siRNA-transfected VSMCs (Figure 1, P <0.05). We also observed that pretreated cells with TLR4 siRNA or the PI3K inhibitor LY294002 could markedly block PI3K/Akt pathway activation and VSMCs migration mediated by HMGB1 ( P both<0.05). Conclusion: These data provide the first evidence that HMGB1-induced VSMCs migration is mediated through a TLR4-dependent PI3K/Akt signaling pathway, which suggest a possible molecular mechanism for HMGB1 may contribute to neointima formation after vascular damage.