| In pork production,percentage of lean meat is often closely related to meat quality,but excessive lipid deposition will greatly reduce lean meat percentage,affecting the pork flavor and quality.Fat deposition also affects the reproductive performance of pig.For humans,excessive lipid deposition can increase the prevalence of obesity and affects the health of our body.Therefore,it is urgent to find a safe and effective anti-lipid deposition strategy.On one hand,it can be applied to pork production to provide a theoretical basis for improving lean meat percentage and improving meat quality;on the other hand,it can provid new strategies for treating obesity and its corresponding complications.Lactucin is a natural compound derived from Chicory.It belongs to sesquiterpene lactone compounds and exhibits the benefical properties of antibacterial,antimalarial,anti-insomnia and fatty liver.In this study,the effects of lactucin on the lipid deposition were evaluated in mice and in cultured adipocytes.1.The effect of lactucin on the lipid deposition in mice.High-fat diet fed mice were administrated with a solution of 20 mg/kg/d of lactucin for 7 weeks.Body weight and food intake were recorded every day,insulin sensitivity and glucose tolerance experiments were also performed.After 7 weeks,mouse adipose tissue was collected and weighed,then tissue sections were performed,and the RNA and protein expression of genes involved in lipid synthesis were measured.The results showed that lactucin treatment reduced the body weight(P <0.05)and fat mass(P <0.05)of high-fat diet fed mice,and did not affect food intake and TG content in feces(P> 0.05).At the same time,the levels of TG and LDL in the serum of the mice were significantly lower in lactucin-treated group than in controls(P <0.05),and the number of adipocytes in adipose tissue was also significantly lower in lactucin-treated group than in controls(P <0.05).Similarly,the m RNA and protein levels of PPAR γ,C/EBP α and C/EBP β that related to TG synthesis(P <0.05)were also lower in lactucin-treated group than in controls,as of the expression of JAK2/STAT3 signaling(P <0.05).In addition,lactucin treatment also improves the insulin sensitivity and glucose tolerance of high-fat diet fed mice(P <0.05),and reduces the expression of ACC and FAS in the liver(P <0.05).Together,these results showed that lactucin treatment inhibits lipid deposition and improves glucose homeostasis in mice.The effect may be related to the JAK2/STAT3 signaling pathway.2.Lactucin treatment inhibits adipogenesis in 3T3-L1 cells by downregulating JAK2/STAT3-mediated mitotic clone expansion.First,3T3-L1 cells were treated with lactucin at different concentrations to detect cell viability.The results showed that lactucin(≤ 80 μM)did not markedly affect cell viability(P > 0.05);then cells were treated with 20 μM.Oil red O staining showed that lactucin-treated cells had less lipid accumulation during differentiation than that of vehicle controls(P <0.05).Consistently,the expression levels of lipid synthesis-related genes(PPAR γ,C/EBP α,C/EBP β,ect)were markedly lower in lactucin-treated cells than in controls(P <0.05).Flow cytometry results showed that the treated cells were unable to undergo mitotic clone expansion(MCE)(P <0.05),suggesting that lactucin treatment may play an inhibitory role in the early stages of adipogenesis.Further research showed that the lactucin-induced MCE arrest may be caused by the decrease of the expression of the JAK2/STAT3 signaling pathway(P <0.05).Subsequently,the cells were co-treated with colivelin(a specific activator of STAT3)and lactucin.Compared with the lactucin-treated group,MCE arrest was relieved in co-treated groups(P <0.05),and the lipid accumulation was also increased(P <0.05).Also,the expression of lipid synthesis-related genes PPAR γ,C/EBP α and C/EBP β were significantly increased(P <0.05),and the expression of JAK2/STAT3 signaling pathway was also increased.Together,these results showed that lactucin treatment inhibits adipogenesis in vitro by downregulation of the JAK2/STAT3 signaling pathway-mediated mitotic clones expansion.3.Effects of lactucin on IL-6/GP130-related signaling pathways.At the late stage of 3T3-L1 cell differentiation,20 μM lactucin was added into medium.The result showed that late stage treatment of cells by lactucin promotes lipolysis.Then,the expression levels of ATGL and HSL,as well as the released plasma content of FFA in the medium were detected.The results showed that lactucin treatment could significantly promote the expression of ATGL and HSL(P <0.05),and the content of FFA in the medium was also significantly increased(P <0.05).By informatic analysis,the target site of lactucin was predicted to be GP130.Therefore,the expression of IL-6,IL-6R,GP130,and ATX were detected.The results showed that lactucin treatment promotes the m RNA and protein expression of these genes(P <0.05).In order to test whether the target of lactucin is GP130 in adipocytes,cells were treated with the specific inhibitor(SC144)of GP130.Oil Red O staining showed that SC144 treament could alleviate the promotive effect of lactucin on lipolysis(P <0.05),and as well as the subsequent FFA release in the medium(P <0.05).The protein and m RNA expressions of related genes were detected,and the results showed that the expressions of IL-6,ATGL and ATX were all decreased when compared to lactucin alone treated group(P <0.05),while other genes were not markedly changed(P > 0.05).Together,these results showed that the effect of lactucin on lipolysis may be related to IL-6/GP130-related signaling pathways.In summary,our study showed that in vivo,lactucin treatment inhibits lipid deposition,improves fatty liver and glucose homeostasis.In vitro,lactucin treatment affects adipogenesis by inhibiting JAK2/STAT3-mediated MCE.Lactucin treatment of late differentiation stage of adipocytes promotes lipolysis through IL-6/GP130-related signaling pathways. |
