The Regulation Of Leptin On The Expression Of PPARgamma In Hepatic Stellate Cell

Objective The study was designed to observe the effects ofleptin on the expression of PPARgamma in primary rat HSC and toreveal the mechanisms of the effects.Methods In Vivo: C57BL/6J ob/ob mice, a naturallyoccurring leptin deficient animal, were given NS (0.5ml,3timesper week), TAA(200μg·g-1,3times per week) or TAA(200μg·g-1,3times per week) plus leptin (1μg·g-1·d-1),intraperitoneally (IP)for1to4weeks. Sirius red staining was used to observe the levelsof fibrosis. The expressions of PPARgamma protein in HSC wereassessed by using enzyme immunohistochemistry and double-labelimmunofluorescence. In Vitro: Hepatic stellate cells were isolatedfrom SD rat liver tissue, then treated HSC with leptin. Theexpressions of PPARgamma protein in HSC were assessed byusing Western-blot. Using methods (such as transfection) toinfluence the signaling pathways which were activated by leptin,the effect of leptin on PPARgamma gene expression in primarycultured rat HSCs was assess and the related mechanisms wereinvestigated. Using PPARgamma inhibitor to inhibit the activity ofPPARgamma, the expressions of HSC division-related proteinwere assessed by Western-blot, showing the functional significanceof the inhibitory effect of leptin on the expression of PPARgammain HSC. Statistical analysis: Differences between groups were evaluated by t-test. Where appropriate, comparisons of multipletreatment conditions with controls were analyzed by ANOVA. Theratio between specific protein expression and restricted referencematerials was analyzed by Stata7.0.Results In Vivo: Liver biopsy with sirius red stainingshowed: after4weeks of different treatments, the group givenTAA puls leptin showed a more visible collagen fibers while theother two had no obvious change. Enzyme immunohistochemistryon liver biopsy showed: TAA group clearly showed PPARgammareactivity in perisinusoidal cells with stellate projections, andalmost no PPARgamma-positive perisinusoidal cells with stellateprojections could be detected in liver biopsy of TAA plus leptingroup. Subsequent double-label immunofluorescence showed:leptin inhibited PPARgamma expression in HSC in hepatic fibrosismodel. In Vitro: The result of Western-blot showed the obviouslyinhibitory effect of leptin on PPARgamma expression in HSC.Mechanisms: The inhibitory effect of leptin on the expression ofPPARgamma protein and the activity of PPARgamma genepromoter in HSC was at least partly through activating PI-3K/AKTand ERK signaling pathways. The effect of leptin on PPARgammain HSC up-regulated the expression of Cyclin D1which promotescell division, down-regulated the expression of p21which inhibitscell division.Conclusion1. Leptin inhibits PPARgamma expression inHSC in vitro and in vivo.2. Leptin down-regulates PPARgammaexpression at least partly through activation of PI-3K/AKT or ERKsignaling pathway in primary cultured rat HSC.3. The inhibitoryeffect of leptin on the expression of PPARgamma in HSC promotesthe division of HSC.