The Role Of Hepatic X Receptor Signaling In Tamoxifen In Mediating Non-alcoholic Fatty Liver Disease And The Effect Of Vitamin D Intervention

Tamoxifen is an FDA-approved first-line treatment for estrogen-receptor-positive breast cancer.Tamoxifen aims to treat breast cancer by competing with estrogen for estrogen receptors,inhibiting estrogen receptor activation and transcriptional activation of downstream target genes.With the widespread use of tamoxifen,studies have found a range of side effects in treating breast cancer,including endometrial cancer,depression and energy-metabolism disorders.The disease of energy metabolism disorders is represented by nonalcoholic fatty liver disease.C linical trials have demonstrated that long-term use of tamoxifen in the treatment of breast cancer significantly increases the risk of NAFLD in breast cancer patients.TAM induced fatty liver after inhibiting estrogen receptor activity,suggesting that ER signaling pathway is involved in TAM induced NAFLD,but the specific mechanism is still unclear.A large number of studies have shown that LXR,as a member of the orphan receptor family,plays a crucial role in various energy metabolism processes,including lipid metabolism,cholesterol metabolism,etc.,but the role of LXR in TAM induced NAFLD has not been known.Vitamin D is a common fat-soluble vitamin that can be obtained from sunlight or food.C linical studies have shown a negative correlation between vitamin D levels in vivo and the incidence of fatty liver disease,and experimental studies have also confirmed that vitamin D can relieve non-alcoholic fatty liver disease.But it is not known whether vitamin D has the same effect on drug-induced nonalcoholic fatty liver disease.Therefore,to determine whether vitamin D can interfere with tamoxifen-induced nonalcoholic fatty liver disease and its mechanism of action may provide a possible intervention for clinical prevention of the side effects of tamoxifen in the treatment of breast cancer.Objective: In this study,female C57BL/6 mice were used as an in vivo model and human hepatoma cell Line HepG2 was used as an in vitro model.From the perspective of nuclear receptor,the mechanism of TAM on liver lipid metabolism and the mechanism of VD on lipid metabolism disorder were discussed,providing more experimental evidence for nutritional intervention of non-alcoholic fatty liver caused by breast cancer treated with TAM.Methods: Triglyceride detection kit and oil red O staining were used to detect the triglyceride content in HepG2 cells and liver tissues of mice.Real-time quantitative PCR was used to detect the expression of Srebp-1c both in vivo and in vitro.The binding of estrogen receptor to liver X receptor and the binding of p300 and NCOR to estrogen receptor/liver X receptor complex were detected by protein immunoprecipitation assay.Results: 一、The role of ER/LXR complex in TAM induced hepatic lipid metabolism disorder 1.Effects of TAM on basal indicators in mice: Female C57BL/6 mice were randomly divided into 3 groups: Normal diet group(ND),Tamoxifen group(TAM)and Tamoxifen+Vitamin D group(TAM+VD),10 mice were fed in each group for 15 weeks..The results showed that TAM reduced the food intake of mice and reduced body weight without affecting liver weight.2.Effect of TAM on lipid metabolism in mouse liver: TAM up-regulated the expression of lipid-forming gene Srebp-1c in mouse liver tissues,and promoted the accumulation of TG in mouse liver tissues.3.Effect of TAM on lipid metabolism in vitro: Providing a low dose of oleic acid(0.1m M)as the raw material,TAM was treated with 10 μM TAM for 24 h.Compared with the control group,TAM induced TG accumulation in HepG2 cells by promoting the expression of Srebp-1c.4.The effects of ER/LXR signaling pathways in TAM induced in vitro cell the role of lipid metabolic disorders: ER and LXR/RXR heterologous dimers combine to form a multivariate receptor complexes,TAM does not directly affect the adhesion strength of the ER/LXR complexes,but by promoting ER/LXR complex NCOR disintegrate and p300 recruiting to raise the expression of Srebp-1c,thereby promoting TG accumulation in HepG2 cel s.二、The role of ER/LXR complex in VD in alleviating TAM induced hepatic lipid metabolism disorder 1.Effects of VD on basic indicators in mice: VD did not affect the reduction of food intake and body weight caused by TAM in mice,and it had no effect on liver weight of mice.2.Effects of VD on TAM induced liver lipid metabolism disorder in mice: VD can inhibit the increase of TAM induced expression of Srebp-1c and alleviate the deposition of TG mediated by TAM in the liver tissues.3.In vitro model,the effect of 1,25 D on TAM induced hepatic lipid metabolism disorder: 1,25 D inhibited the TAM-induced increase of Srebp-1c expression and reduced the accumulation of TG in HepG2 cells.4.The role of ER/LXR signaling pathway in 1,25 D alleviating TAM induced lipid metabolism disorder in vitro: 1,25 D does not affect the binding ability of ER and LXR,but reducing the expression of Srebp-1c by promoting the dissociation of p300 and the recruitment of NCOR on ER/LXR complex,thus al eviating TAM mediated lipid metabolism disorder.Conclusion: In this study,HepG2 cells were used as a vitro model and C57BL/6 mice as a vivo model.It was found that TAM induced hepatic lipid metabolism disorder by promoting the dissociation of NCOR and the recruitment of p300 on ER/LXR complex to up-regulate the expression of Srebp-1c.In addition,VD alleviates hepatic lipid metabolism disorder by promoting the dissociation of p300 and the recruitment of NCOR on ER/LXR complex to inhibit the increase of Srebp-1c expression caused by TAM.