Angiotensin (Ang II) plays an important role in atherosclerosis through proinflammatory effect. Toll-like receptor 4 (TLR4) may mediate inflammatory response. It is unknown whether TLR4 mediates the proinflammatory effect of Ang II. Thus, we observed the role and signaling pathway of TLR4 in Ang II-induced inflammation in rat vascular smooth muscle cells (VSMCs). Ang II and LPS stimulated TNF-α secretion and inhibited 6-keto-PGF 1α production, upregulated MMP-9 and downregulated PPARγ and PPARα

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... in rat VSMCs. Ang II also distinctly upregulated TLR4 expression in the cells. Pretreatment of the cells with anti-TLR4 antibody prior to Ang II stimulation significantly diminished the effects of Ang II. These suggest that Ang II stimulates VSMCs to produce inflammation through regulation of the proinflammatory and the antiinflammtory factors via TLR4-dependent mechanism. The further investigations showed that AT1 receptor antagonist losartan or ERK1/2 inhibitor PD098059 inhibited Ang II-induced TLR4 expression, TLR4 inhibitor prevented Ang II-induced IP-10 expression, anti-IP-10 antibody partly abolished Ang II-induced PKC increase, and PKC inhibitor chelerythrine suppressed Ang II-induced NF-κ B expression. These demonstrate that TLR4-mediated proinflammatory effect of Ang II in VSMCs involves AT1/ERK1/2/TLR4/IP-10/ PKC/NF-κB pathway. Our results provide the evidence that Ang II induces inflammatory response involved in pathogenesis of atherosclerosis partly via TLR4-dependent signaling pathway in VSMCs.