Inhibitory Effect of Luteolin on Hepatic Stellate Cell Activation Is STAT3 Dependent

Abstract

IntroductionSTAT3 is activated in a majority of cancer and other fast growing cells, such as activated hepatic stellate cells (HSC), which are the primary effector of liver fibrosis. Tyr705 phosphorylation of STAT3 is a key step for its function, so it has become a widely explored target for new drug development. Luteolin is an important member of the flavonoid family and has anti‐tumorigenic, anti‐oxidant, and anti‐inflammatory properties. Previously, we have reported that luteolin has a significant anti‐fibrogenic effect on activated HSC. However, its molecular mechanisms remain unclear. In this present study, we determined the role of STAT3 on luteolin‐induced HSC inactivation.MethodsThe activated human and rat hepatic stellate cell lines LX‐2 and HSC‐T6 were used for this study. Cellular proteins were analyzed by immunoblotting and immunofluorescence. Cell proliferation following STAT3 inhibitors treatment was assessed with Alamar Blue assay.ResultsLuteolin treatment significantly inhibited pSTAT3 (Tyr705) protein expression (p<0.001) in both a time‐ and dose‐dependent manner by immunoblot assay and confirmed by immunofluorescence staining. Additionally, luteolin suppressed pSTAT3 nuclear translocation (p=0.009) and its transcriptional activity (p=0.03). The downstream effectors of STAT3 pathway, c‐Myc and cyclin D1, were inhibited by luteolin treatment (p<0.0001). Importantly, treatment with STAT3 inhibitors, Stattic and SH‐4‐54, resulted in a marked decrease in LX‐2 cell growth and expression of HSC activation marker α‐smooth muscle actin, which was similar following luteolin treatment.ConclusionLuteolin treatment inhibited STAT3 signaling and its target genes. STAT3 inhibitors attenuate LX‐2 cell growth and activation. Luteolin may affect HSC activation through the STAT3 pathway.Support or Funding InformationNational Institutes of Health: T32‐GM8256