Zhilong Huoxue Tongyu Capsule regulates the macrophage polarization and inflammatory response via the let-7i/TLR9/MyD88 signaling pathway

Zhilong Huoxue Tongyu Capsule (ZL) is clinically prescribed for acute ischemic stroke (AIS). However, only a few studies have addressed the mechanisms of ZL in treating AIS. To explore the underlying mechanism of macrophage polarization and inflammation mediated by ZL, and to provide a reference for AIS treatment. Sixteen SD rats were fed with different dose of ZL (0, 0.4, 0.8, and 1.6 g/kg/d) for 4 days to prepare ZL serum. After 500 ng/mL lipopolysaccharide (LPS) stimulation, RAW264.7 cells were administrated with ZL serum. Then, experiments including ELISA, flow cytometry, real-time quantitative PCR and western blot were performed to verify the effects of ZL on macrophage polarization and inflammation. Next, let-7i inhibitor was transfected in RAW264.7 cells when treated with LPS and ZL serum to verify the regulation of ZL on the let-7i/TLR9/MyD88 signaling pathway. Moreover, the interaction between let-7i and TLR9 was confirmed by the dual-luciferase assay. ZL serum significantly decreased the expression of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α), and increased the expression of IL-10 and transforming growth factor β1 (TGF-β1) of LPS stimulated-macrophages. Furthermore, ZL serum polarized macrophages toward M2, decreased the expressions of TLR9, MyD88, and iNOS, as well as increased the expressions of let-7i, CHIL3, and Arginase-1. It is worth mentioning that the effect of ZL serum is dose-dependent. However, let-7i inhibitor restored all the above effects in LPS stimulated-macrophages. In addition, TLR9 was the target of let-7i. ZL targeted let-7i to inhibit TLR9 expression, thereby inhibiting the activation of the TLR9/MyD88 pathway, promoting the M2 polarization, and inhibiting the development of inflammation in AIS.