Effect And Mechanism Of Curcumin On Adipogenic Differentiation Of Porcine Subcutaneous Preadipocytes

Intramuscular fat content and backfat thickness are important economic characteristics for evaluating pork quality.The backfat thickness mainly depends on the content of subcutaneous fat.Therefore,without affecting the flavor and quality of pork,reducing the amount of subcutaneous fat deposits is an important economic trait for pigs.One of the key indicators for evaluating pork quality is fat content.The direct correlation between subcutaneous fat content and economic value and meat quality is a key measure for pork quality control.Curcumin(CUR)is a natural polyphenolic active substance extracted from the rhizome of the plant turmeric.It has many biological functions such as lowering blood lipids and improving lipid metabolism.However,its regulatory role in adipogenic differentiation of subcutaneous porcine preadipocytes(PSPA)is not yet clear,and its molecular mechanism also needs to be further revealed.This study includes following the four parts.1.The effect of curcumin on the glucose uptake and adipogenic differentiation of PSPA.This experiment used PSPA as a model to explore the effect of CUR on the glucose uptake and differentiation of PSPA.The results showed that,treatments with low concentrations of CUR(10,15,20 μmol/L)had no significant effect on the proliferation and cytotoxicity of PSPA,however,high concentration of CUR(30μmol/L)treatment significantly inhibited the cell proliferation and cytotoxicity.In addition,the glucose consumption,the intracellular TG content and the activity of G3PDH was significantly reduced in CUR treated cells,indicating that CUR had a inhibitory effect on the glucose uptake and adipogenic differentiation of PSPA.2.Molecular mechanism of curcumin on inhibiting glucose uptake and differentiation of PSPA.This experiment continued to use PSPA as a model to further explore the mechanism of low concentration of CUR in inhibiting the glucose uptake and adipogenic differentiation.The results are as follows:CUR treatment significantly inhibited the mRNA expression and phosphorylation level of ERK1/2.In addition,the key transcription factors PPAR-y,C/EBP-α and SREBP-1c for adipocyte differentiation downstream of ERK1/2,fatty acid synthesis rate-limiting enzymes FAS and ACC,fatty acid binding protein AP2 and glucose transporter GLUT4 expression,and PPAR-γ transcription activity decreased significantly in the CUR treatment group,while the expression of Pref-1 increased significantly.The above results indicate that CUR may inhibit the differentiation of PSPA by inhibiting the ERK1/2-PPAR-γsignaling pathway.Therefore,this part of the experiment further explored the "torsion"effect of ERK pathway activation(FGF-2 pretreatment for 30 min)on CUR’s inhibition of differentiation.The results showed that compared with the DM+CUR group,the phosphorylation level of ERK1/2 in the FGF-2+DM+CUR group was significantly increased,and the expressions of PPAR-y,C/EBP-γ,FAS,ACC and GLUT4 were also significant increased,while TG content and cell supernatant glucose consumption decreased significantly.It shows that low concentrations of CUR mainly inhibit the ERKl/2-PPAR-y pathway,inhibit the glucose consumption and differentiation of PSPA,and then reduce the lipid deposition in pig fat cells.3.Curcumin inhibits the adipogenic differentiation of PSPA by promoting apoptosis.In this part of the experiment,high-concentration CUR was selected to explore the role of adipocyte apoptosis in inhibiting the adipogenic differentiation of PSPA undertreatment of CUR.The results showed that the expression of the BCL-2 was significantly reduced in the CUR treated cells,and the expression of the BAX and the ratio of BAX/BCL-2 were both significantly increased.In addition,the expression of Caspases-3,-8,-9 and Cleaved-caspases-3,-8,-9 in the CUR treated cells were all significantly increased.However,our repeated experiments on 3T3-L1 also reached the same conclusion.The results showed that CUR can block PSPA in S and G2/M phases to inhibit the cell proliferation.Furthermore,the expression of the BAX and the apoptosis rate were increased significantly.These above results indicate that high concentration of CUR can promote the apoptosis of PSPA by activating the apoptosis pathway.4.Effect of curcumin on alleviating lipid deposition in high-fat diet mice.Based on the above in vitro results,which demonstrated that CUR was able to inhibit the glucose uptake and adipogenic differentiation,we next explored whether CUR can regulate lipid deposition at the in vivo level.The experiment used high-fat-induced C57BL/6J obese mice as a model,and added different concentrations of CUR to the diet to observe its effect on lipid deposition in mice.The results showed that dietary supplementation of CUR can reduce blood glucose content,serum insulin level and the content of TG and TCHO in epididymal fat and liver tissue,significantly enhance the glucose tolerance.In addition,CUR treatment reduced the content of TG and the liver glycogen content.The average area,circumference and volume of epididymal adipocytes were also significantly reduced.The above results indicate that the addition of CUR can significantly improve excessive lipid deposition induced by high-fat diet.In summary,the present results showed that low concentrations of CUR can inhibit adipocyte glucose uptake and adipogenic differentiation by inhibiting the ERK1/2-PPAR-γ signaling pathway,thereby inhibiting the de novo synthesis of fatty acids and repressing lipid deposition.High concentration of CUR can trigger apoptosis by increasing the ratio of BAX/BCL-2 and the expression of Caspases-3,-8 and-9.These above results provide a theoretical basis for the application of CUR as a safe and effective new type of green feed additive for lowering lipids in animal husbandry and veterinary production.