Angiotensin II induces toll-like receptor 4 expression and myeloperoxidase activity in RAW264.7 cells

AIM: To investigate the effects of angiotensin II (Ang II) on mRNA and protein expressions of toll-like receptor 4 (TLR4) and myeloperoxidase (MPO) activity in RAW264.7 cells, and explore its pro-inflammatory and pro-atherosclerotic mechanisms. METHODS: Murine RAW264.7 cells were cultured and stimulated with different concentrations (1, 10, 100 and 1,000 nmol/L) of Ang II or LPS (100 microg/L) for 24 h. TLR4 mRNA levels were analyzed by RT-PCR, and TLR4 protein expression was measured by Western blot. MPO activity in the supernatant was assayed with colorimetry. Then, the cells were pretreated with TLR4 blocker (1 and 5 mg/L) for 1 h prior to stimulation with 100 nmol/L Ang II for 24 h, and MPO activity in the supernatant was detected. RESULTS: Ang II increased mRNA and protein expressions of TLR4 in RAW264.7 cells in concentration-dependent manner (P<0.01), and LPS also induced mRNA and protein expressions of TLR4 in RAW264.7 cells (P<0.01). In addition, Ang II concentration-dependently elevated MPO activity in RAW264.7 cells (P<0.01), and LPS also enhanced MPO activity of RAW264.7 cells (P<0.01), but the TLR4 blocker significantly antagonized the effect of Ang II on MPO activity (P<0.01). CONCLUSION: Ang II upregulates TLR4 expressions, and induces MPO secretion via TLR4 in RAW264.7 cells, which mediate the pro-inflammatory effect of Ang II to contribute formation and development of atherosclerosis.