Vitamin C Down-regulate Apo(a) Expression Via TET2-dependent Demethylation Of ELK1 Promoter In HepG2 Cells

[Background] Level of human plasma lipoprotein(a)[Lp(a)] related closely to development of atherosclerosis.A large number of studies have shown that high plasma lipoprotein(a)would increase the risk of atherosclerosis.Epidemiological survey found that there are 25 percent people with a higher plasma lipoprotein(a)level than others.There is no drug can reduce specially the concentrations of plasma lipoprotein(a).So,it is especially important to research the new drug to decrease specially plasma lipoprotein(a)level.Recent studies showed that vitamin C can reduce the levels of plasma lipoprotein(a)in transgenic mice,but the specific mechanism is unclear.Several studies also found that lipoprotein(a)structure is mainly composed of an apolipoprotein(a),[apo(a)] and a low density lipoprotein(LDL)core components,and apo(a)bond with the apolipoprotein B-100(apoB100)on LDL core by disulfide.The apo(a)is a specific component of lipoprotein(a),and are the limiting factors of lipoprotein(a)synthesis.So,we hypothesized that vitamin C limit synthesis of lipoprotein(a)by decreasing the apo(a)synthesis,to further lowering plasma lipoprotein(a)level.[Objective] Investigate the effects of vitamin C on apo(a)expression and the possible molecular mechanism of vitamin C influencingapolipoprotein(a)[apo(a)] biosynthesis in HepG2 cells.[Methods] HepG2 cells were incubated with 800μM vitamin C for 0,6,12,18,24 h or 0,200,400,600,800μM vitamin C for 24 h to investigate the effects of vitamin C on apo(a)expression.Using small interfering RNA(siRNA)transfection,real-time fluorescent quantitative PCR,western blot,CHIP assay,DNA immunoprecipitation-qPCR,Dot-blot assay,ELISA investigate the mechanism of vitamin C regulating the apo(a)expression.[Results] 0-400μM vitamin C can promote the apo(a)expression and 400-800μM vitamin C can inhibit the apo(a)expression;vitamin C can also increase ELK1 expression and hydroxy-methylation of ELK1 promoter and the globle DNA in in HepG2 cells;the effects of vitamin C inhibiting the apo(a)expression were attenuated by ELK1 siRNA and TET2 siRNA.[Conclusion] 400-800μM vitamin C can inhibit the apo(a)expression via TET2-dependent demethylation of ELK1 promoter in HepG2 cells.