The Mechanism Of Curcumin Accelerating LDL-C Uptaked In HepG2 Cells

Objective: To explore the molecular mechanisms of upregulated LDL-C uptake of Hep G2 cells treated with Curcumin, and to clarify the functions of Curcumin in lipid-lowering and slowing the atherosclerosis process. Expect to provide a scientific basis for Curcumin as a lipid-lowering drug in clinical development.Method: Hep G2 cells were incubated with 1% penicillin- streptomycin mixture and 10% FBS DMEM medium for 24 hours, after that, changed medium and added with 25 mg/L LDL and Curcumin for 24 hours. Oil red O staining is used to observe Hep G2 cells after lipid uptaked. Enzymatic method is used to determine the content of intracellular free cholesterol and total cholesterol. To detect fluorescence intensity after incubated by Di I labeled LDL. The LDLR levels on the surface of cell membrane were detected by immunofluorescence flow cytometry. The m RNA expressions of LDLR, SREBP2 and HMGCR are analyzed by RT-Q-PCR. Western blot is used to analyze the protein levels of LDLR, SREBP2, HMGCR, PCSK9 and IDOL.Results:1. The results of oil red O staining showed that Hep G2 cells have more lipid droplets content in Control than Basal, and there is no significant difference between Control and Vehicle. Compared with Control, the rate of oil red O-positive cells and the number of red lipid droplets were significantly increased in Curcumin group.2. Compared with Basal group, the levels of TC and FC increased in Control. Compared with Control, the levels of TC and FC increased in Vehicle group(P >0.05), but Curcumin group had a significantly increased(P <0.01). Those results showed that Vehicle had no effect on the intracellular TC and FC levels, but Curcumin can increase the levels of TC and FC in Hep G2 cells.3. The results of Di I-LDL uptake experiment showed that fluorescence intensity was enhanced in LPDS and Curcumin groups versus to the Control. 25-HC group was reduced. Our results suggest that Curcumin promotes LDL uptake in Hep G2 cells.4. The results of immunofluorescence flow showed that Curcumin increased the LDLR levels in Hep G2 cells membrane.5. The results of RT-Q-PCR and western blot showed that cucumin significantly upregulate the expression of LDLR, SREBP2 and HMGCR m RNAs and proteins in Hep G2 cells, what's more,mature PCSK9 and IDOL protein levels were significantly increased.Our results suggest that cucumin upregulates the expression of SREBP2 and LDLR. On the other hand, Curcumin reduces the proteins expression of PCSK9 and IDOL, thereby decreases the LDLR degradation. Two aspects co-upregulate the protein expression of LDLR, promote LDL uptake in Hep G2 cells and increase intracellular lipid droplets and free and total cholesterol contents.Conclusion: Curcumin accelerates LDL-C uptake probably via downregulate the protein expression of PCSK9 and IDOL in Hep G2 cells.