| Fat metabolism is an important part of the body’s normal energy metabolism, lipidmetabolism imbalance can cause fatty deposits, even obesity. Obesity can lead to a variety ofmetabolic diseases, including insulin resistance, fatty liver, hypertension, cardiovasculardisease, diabetes and cancer, silent information regulator1(Sirt1), an candidate factors ofobesity, is associated with many metabolic diseases, so researching the signaling pathway andthe metabolic processes that are regulated by Sirt1are important. We aimed at exploring theeffects of mTOR signaling pathway in the regulation processes of Sirt1on fat metabolism invivo and in vitro. Km mice and primary adipocytes were the study subjects. Body weight,subcutaneous fat pads, epididymal fat pads and perirenal fat pads were weighed. Levels ofTotal cholesterol(TC), triglycerides(TG), high density lipoproteincholesterol(HDL-C) and lowdensity lipoproteincholesterol(LHDL-C) in serum were measured. Lipase activity in serumwas measured by Lipase Activity Test Kit. Real-time PCR was applied to detect theexpression levels of Sirt1, adipose metabolism related genes and the key regulator factor ofmTOR signal pathway. The protein levels of adipose metabolism related genes and the keyregulator factor of mTOR signal pathway were detected by Western blotting. The main resultswere summarized as follows:1.Comparing with control group, activation of Sirt1by resveratrol can attenuate theincrease of body mass and body fat mass, the concentrations of TG, TC and LDL-C in serumwere decreased significantly, and the level of HDL-C was increased. Lipase activities inserum was significantly activated. The expression levels of FAS mRNA were reduced inmouse epididymis fat tissue, liver and muscle, but the level of FAS mRNA was not notable inbrown adipose tissue, PPAR γ and SREBP1mRNA levels were down-regulated, ATGL, HSL,Perilipin, and Sirt1mRNA levels were up-regulated, mTOR, S6K1and4EBP1mRNA levelswere also down-regulated; Nicotinamide treated mice, the body mass, epididymal fat andsubcutaneous fat mass were slowly increased, perirenal fat mass was increased, theconcentrations of LDL-C was up-regulated, the levels of HDL-C and LPS activity weredown-regulated. The expression levels of PPAR γ and SREBP1were in creased in thesetissues, FAS mRNA levels in liver and muscle were increased significantly, but they were not notable in epididymal fat and Brown fat tissues, ATGL, HSL, Perilipin, and Sirt1mRNAlevels were down-regulated, mTOR, S6K1and4EBP1mRNA levels were up-regulated in allthe tissues. The Western Blotting results showed that resveratrol down-regulated theexpression of FAS protein, up-regulated the expression of ATGL protein and thephosphorylation of mTOR and S6K1protein; nicotinamide reduced the levels of ATGL proteinand increased the phosphorylation of mTOR and S6K1protein, but it had no effect on theexpression of FAS protein. All the results indicated that activation of Sirt1could reduce the fatmass synthesis rate, increase the fat decomposition rate and inhibit the activity of mTORsignaling pathway, finally reduce fat deposition.2.In high-fat diet induced obese mice, activation of Sirt1by resveratrol could effectivelycontrol body weight, perirenal fat, epididymis fat and subcutaneous fat mass weresignificantly lower than control group, the concentrations of TG, TC and LDL-C in serumwere decreased significantly, and the level of HDL-C was increased，lipase activities wasincreased. The expression levels of PPAR γ, SREBP1and FAS mRNA were down-regulatedin these tissues, but the levels of FAS mRNA as the same as control group in muscle, ATGL,HSL, Perilipin, and Sirt1mRNA levels were up-regulated, mTOR, S6K1and4EBP1mRNAlevels were down-regulated; inhibition of Sirt1by nicotinamide increased the body weight,Perirenal fat and epididymal fat mass were increased, the concentrations of TG and LDL-Cwere increased, the level of HDL-C was reduced, The expression levels of PPARγ, SREBP1and FAS mRNA were up-regulated, but the level of FAS mRNA was not effected in muscle,ATGL, HSL, Perilipin, and Sirt1mRNA levels were down-regulated, mTOR, S6K1and4EBP1mRNA levels were up-regulated in these tissues.In western blotting results, resveratroldown-regulated the expression of FAS protein, up-regulated the expression of ATGL proteinand the phosphorylation of mTOR and S6K1protein; nicotinamide reduced the levels of ATGLprotein, increased the expression of FAS protein and the phosphorylation of mTOR and S6K1protein. The results reveal that activation of Sirt1could inhibit mTOR signaling pathway andfat deposition in obese mice, Inhibition of Sirt1could promote fat synthesis and activatemTOR signaling pathway.3.In primary adipocytes, activation of Sirt1by resveratrol significantly inhibited theexpression of mTOR, S6K1and4EBP1, both in mRNA and phosphorylation levels, ATGL,HSL, Perilipin mRNA levels were up-regulated, the expression of ATGL protein wasincreased, the expression levels of PPAR γ, SREBP1and FAS mRNA were down-regulated,the expression of FAS protein was reduced; Inhibition of Sirt1by nicotinamide increased theexpression of mTOR, S6K1and4EBP1, in mRNA and phosphorylation levels, the expressionlevels of PPAR γ, SREBP1and FAS mRNA were up-regulated, the expression of FAS protein was increased, ATGL, HSL, Perilipin mRNA levels were down-regulated, theexpression of ATGL protein was reduced; We also found that Leucine could partly recoverythe inhibition of Sirt1on mTOR signaling pathway and fat deposition, rapamycin could partlyreverse the role of Sirt1; These results suggesting that Sirt1could suppress fat depositionthrough mTOR signaling pathway, at least partly through mTOR signaling pathway. |
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