Schisandrin B suppresses TGFβ1-induced stress fiber formation by inhibiting myosin light chain phosphorylation

Schisandra chinensis fruit extract (SCE) has been used as a traditional oriental medicine for treating vascular diseases. However, the pharmacologic effects and mechanisms of SCE on vascular fibrosis are still largely unknown. Transforming growth factor β1 (TGFβ1)-mediated cellular changes are closely associated with the pathogenesis of vascular fibrotic diseases. Particularly, TGFβ1 induces actin stress fiber formation that is a crucial mechanism underlying vascular smooth muscle cell (VSMC) migration in response to vascular injury. In this study, we investigated the effect of SCE and its active ingredients on TGFβ1-induced stress fiber assembly in A7r5 VSMCs.To investigate pharmacological actions of SCE and its ingredients on TGFβ1-treated VSMCs, we have employed molecular and cell biological technologies, such as confocal microscopy, fluorescence resonance energy transfer, western blotting, and radiometric enzyme analyses.We found that SCE inhibited TGFβ1-induced stress fiber formation and cell migration. Schisandrin B (SchB) showed the most prominent effect among the active ingredients of SCE tested. SchB reduced TGFβ1-mediated phosphorylation of myosin light chain, and this effect was independent of RhoA/Rho-associated kinase pathway. Fluorescence resonance energy transfer and radiometric enzyme assays confirmed that SchB inhibited myosin light chain kinase activity. We also showed that SchB decreased TGFβ1-mediated induction of α-smooth muscle actin by inhibiting Smad signaling.The present study demonstrates that SCE and its active ingredient SchB suppressed TGFβ1-induced stress fiber formation at the molecular level. Therefore, our findings may help future investigations to develop multi-targeted therapeutic strategies that attenuate VSMC migration and vascular fibrosis.