Objective: To investigate the effects of liver X receptor (LXR) on the expression of fatty acid synthase (FAS) in diabetic liver.
Methods: Sixteen-week-old male db/db mice with C57BL/6 background were administered via gavaging of T0901317 (TO), a LXR synthetic agonist, at the dose of 3 mg x kg(-1) x d(-1) or dimethyl sulfide (DMSO), a vehicle alone for 7 days. Then the mice were killed with their livers taken out to undergo immunohistochemistry to observe the distribution of FAS protein. Human hepatocellular liver carcinoma cell of the line HepG2 were cultured with TO (10 micromol/L) or DMSO for 24 hours. Another HepG2 cells were transfected with mouse FAS promoter-luciferase reporter recombinants with or without pcDNA3.1, LXR expression vector, or an active sterol regulatory element binding protein-1c (SREBP-1c) expression vector for 12 hours. Real-time PCR and Western blotting were used to detect the levels of mRNA and protein of FAS and SREBP-1c respectively. Luciferase reporter assay was utilized to examine the activity of mouse FAS promoter.
Results: FAS was abundantly expressed in the mouse livers, especially in the cytoplasm of liver cells. The FAS mRNA levels of the livers of the db/db mice was about 5.5 times as high as that of the db/m mice (P < 0.01). The FAS protein levels in the livers of db/db and db/m mice treated with TO were 1.7 and 3.5 times higher than those of the control mice (both P < 0.05). The SREBP-1 mRNA levels in the liver of the db/m and db/db mice treated with TO were 2.4 and 2.1 times higher compared with the control mice (P < 0.05, P < 0.01). Luciferase test showed that the FAS promoter activity of the HepG2 cells treated with TO was 1.5 times that of the control cells (P < 0.01). The FAS promoter activities of the HepG2 cells transfected with LXR and SREBP-1c were 1.9 and 1.6 times those of the control cells (botn P < 0.01).
Conclusion: LXRE directly or indirect (via SREBP-lc) upregulates the expression of FAS gene in the diabetic liver. LXR may mediate the lipid accumulation in liver of diabetes.