PLIN2 Mediates Ox-LDL-induced Lipid Accumulation Via ER Stress/SREBP2 In RAW264.7 Macrophages

[Objective] To elucidate the relationship between PLIN2 and SREBP2,and to explore the mechanism of PLIN2 promoting lipid accumulation in macrophages.[Methods] Firstly,50mg/L Ox-LDL was incubated with RAW264.7 macrophages for different time.The protein levels of PLIN2 and SREBP2 were detected by Western blot.Secondly,the cell transfection was used to downregulate the expression of PLIN2 and to upregulate the expression of PLIN2.Then,the cells were treated with 50mg/L Ox-LDL for 24 hours.The expression of SREBP2 and its target gene HMGCR was detected by Western blot.The depositing of lipid was observed by oil Red O staining.After silence and overexpression of PLIN2,the free cholesterol test kit was used to detect the change of free cholesterol,the intracellular GRP78 protein level was detected by Western blot,the cell immunofluorescence technique was used to observe the nuclear translocation of SREBP2.Finally,pre-treating cells with ER stress inhibitor 4-PBA for 2 hours,the protein levels of SREBP2 and HMGCR were detected in lipid loaded macrophages.[Results] After treatment of macrophages with 50mg/L Ox-LDL for different time,the expression of PLIN2 increased with the incubation time.At the same time,the expression of SREBP2 increased to reach the highest level at 24 hours and then decreased.Compared with the control group,the protein levels of SREBP2,HMGCR and intracellular lipid content were decreased on silencing PLIN2;While overexpressing of PLIN2,the levels of these proteins and intracellular lipid content were increased.Compared with the silence of PLIN2,overexpression of PLIN2 increased intracellular free cholesterol and ER free cholesterol.Moreover,the expression of the ER stress marker protein GRP78 was increased,and the activation of SREBP2 was increased and nuclear translocation occured.When cells were treated with the ER stress inhibitor 4-PBA,the expression of SREBP2 and HMGCR in lipid loaded macrophages was decreased.[Conclusion] PLIN2 mediates lipid accumulation in macrophages via SREBP2,which may be related to increased ER stress-induced cholesterol synthesis.