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

Objective The study was designed to observe the effects of leptin on the expression of PPARgamma in primary rat HSC and to reveal the mechanisms of the effects.Methods In Vivo: C57BL/6J ob/ob mice, a naturally occurring leptin deficient animal, were given NS (0.5 ml, 3 times per week ), TAA(200μg·g^-1, 3 times per week) or TAA(200μg·g^-1, 3 times per week) plus leptin (1μg·g^-1·d^-1),intraperitoneally (IP) for 1 to 4 weeks. Sirius red staining was used to observe the levels of fibrosis. The expressions of PPARgamma protein in HSC were assessed by using enzyme immunohistochemistry and double-label immunofluorescence. In Vitro: Hepatic stellate cells were isolated from SD rat liver tissue, then treated HSC with leptin. The expressions of PPARgamma protein in HSC were assessed by using Western-blot. Using methods (such as transfection) to influence the signaling pathways which were activated by leptin, the effect of leptin on PPARgamma gene expression in primary cultured rat HSCs was assess and the related mechanisms were investigated. Using PPARgamma inhibitor to inhibit the activity of PPARgamma, the expressions of HSC division-related protein were assessed by Western-blot, showing the functional significance of the inhibitory effect of leptin on the expression of PPARgamma in HSC. Statistical analysis: Differences between groups were evaluated by t-test. Where appropriate, comparisons of multiple treatment conditions with controls were analyzed by ANOVA. The ratio between specific protein expression and restricted reference materials was analyzed by Stata7.0.Results In Vivo: Liver biopsy with sirius red staining showed: after 4 weeks of different treatments, the group given TAA puls leptin showed a more visible collagen fibers while the other two had no obvious change. Enzyme immunohistochemistry on liver biopsy showed: TAA group clearly showed PPARgamma reactivity in perisinusoidal cells with stellate projections, and almost no PPARgamma-positive perisinusoidal cells with stellate projections could be detected in liver biopsy of TAA plus leptin group. Subsequent double-label immunofluorescence showed: leptin inhibited PPARgamma expression in HSC in hepatic fibrosis model. In Vitro: The result of Western-blot showed the obviously inhibitory effect of leptin on PPARgamma expression in HSC. Mechanisms: The inhibitory effect of leptin on the expression of PPARgamma protein and the activity of PPARgamma gene promoter in HSC was at least partly through activating PI-3K/AKT and ERK signaling pathways. The effect of leptin on PPARgamma in HSC up-regulated the expression of Cyclin D1 which promotes cell division, down-regulated the expression of p21 which inhibits cell division.Conclusion 1. Leptin inhibits PPARgamma expression in HSC in vitro and in vivo. 2. Leptin down-regulates PPARgamma expression at least partly through activation of PI-3K/AKT or ERK signaling pathway in primary cultured rat HSC. 3. The inhibitory effect of leptin on the expression of PPARgamma in HSC promotes the division of HSC.