Effects of curcumin on peroxisome proliferator-activated receptor γ expression and nuclear translocation/redistribution in culture-activated rat hepatic stellate cells

Background The function of peroxisome proliferator-activated receptor γ (PPARγ) in hepatic fibrogenesis remainslargely unknown.Curcumin is a natural substance extracted form Curcuma Longa Linn and has a variety ofpharmacological effects.In this study,the effects of curcumin on the proliferation,activation and apoptosis of rat hepaticstellate cells (HSCs) through PPARγ,signaling were investigated.Methods HSCs were isolated from the normal Sprague Dawley rats through in situ perfusion of the liver with PronaseE and density-gradient centrifugation with Nycodenz.Cells were treated with curcumin,troglitazone,salvianolic acid Bor GW9662.The effect on HSCs proliferation was determined by MTT colorimetry.Total RNA was extracted by TRizolreagent and gene levels were determined by semi-quantitative RT-PCR.Total cellular and nuclear protein were isolatedand separated by 10% sodium dodecy Isulfate polyacrylamide gel electrophoresis.Protein levels were determined byWestern blot.Cell apoptosis was detected by Hoechst 33258 staining.PPARy subcellular distribution was detected byimmunofluorescent staining.The activities of MMP-2 and 9 were measured by Gelatin zymograph assay.Results Curcumin suppressed HSCs proliferation in a dose-dependent manner.As HSCs underwent gradualactivation with culture prolongation the PPARγ nuclear expression level decreased.Curcumin up-regulated PPARγexpression and significantly inhibited the production of α-SMA and collagen I.PPARγ is expressed in the cytoplasm andnucleus and is evenly distributed in HSCs,but accumulated in the nucleus of HSCs and disappeared from cytoplasmafter curcumin treatment.Hoechst 33258 staining showed that curcumin induced the apoptosis of culture-activatedHSCs and significantly increased pro-apoptotic Bax expression and reduced anti-apoptotic Bcl-2 expression.Cyclin D1gene,activated NFκB p65 protein and TGFβR-1 protein expression were down-regulated significantly by curcumin.Theactivities of MMP-2 and MMP-9 were enhanced significantly by curcumin.Conclusions Curcumin can inhibit the proliferation and activation of HSCs,induce the apoptosis of activated HSCsand enhance the activities of MMP-2 and MMP-9.The effects of curcumin are mediated through activating the PPARγsignal transduction pathway and associated with PPARγ nuclear translocation/redistribution.