Tanshinone I inhibits vascular smooth muscle cell proliferation by targeting insulin-like growth factor-1 receptor/phosphatidylinositol-3-kinase signaling pathway.

Vascular smooth muscle cell (VSMC) proliferation plays a critical role in arterial remodeling during various vascular diseases including atherosclerosis and hypertension. Tanshinone I, a major component of Salvia miltiorrhiza, exerts protective effects against cardiovascular diseases. In this study, we investigated the effects of tanshinone I on VSMC proliferation, as well as the underlying mechanisms. We found that this compound inhibited the proliferation of VSMCs in a dose-dependent manner, based on 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) and 5-ethynyl-2'-deoxyuridine (EdU) assays. Western blotting demonstrated that tanshinone I inhibited the expression of proliferation-related proteins, including cyclin-dependent kinase 4 (CDK4), cyclin D3, and cyclin D1, in a dose-dependent manner. Molecular docking showed that this compound docked to the inhibitor-binding site of the insulin-like growth factor 1 (IGF-1) receptor (IGF-1R), and the binding energy between tanshinone I and IGF-1R was -9.021 kcal/mol. Molecular dynamic simulations showed that the IGF-1R-tanshinone I binding was stable. We also found that tanshinone I dose-dependently inhibited IGF-1R activation and its downstream molecules, insulin receptor substrate (IRS)-1, phosphatidylinositol-3-Kinase (PI3K), Akt, glycogen synthase kinase-3 beta (GSK3β), mammalian target of rapamycin (mTOR), 70S6K, and ribosomal protein S6 (RPS6). Notably, activation of IGF-1R by recombinant IGF-1 rescued the activity of IGF-1R and its downstream molecules, and the proliferation of tanshinone I-treated VSMC. In addition, blocking PI3K signaling with LY294002 showed the important role of this pathway in tanshinone I-mediated suppression of VSMC proliferation. Collectively, these data demonstrated that tanshinone I might inhibit VSMC proliferation by inhibiting IGF-1R/PI3K signaling.