雄激素促进CYP7A1基因表达在肝脏胆固醇代谢中的作用及机制研究

High cholesterol is an independent and important risk factor for stroke, coronary heart disease, myocardial infarction and sudden cardiac death. Recent studies have shown that age-related decrease in endogenous androgen in men is not only lead to decreased physical strength and libido but also an important risk factor for lipid dysfunction. In our previous study, we used orchidectomized C57 mice (ORX) as the animal model and found that C57 ORX mice had increased liver fat deposition and cholesterol content, decreased bile acid content and down regulated CYP7A1 expression. In vitro, experiments indicated that testosterone could promote the expression of CYP7A1 gene, and the effects disappeared after addition of androgen receptor antagonist. Therefore, we hypothesized that androgen could promote the expression of CYP7A1 gene via androgen receptor and then accelerate the conversion of cholesterol to bile acid. We will further clarify the specific mechanism of androgen upregulating CYP7A1 gene expression by using the method of molecular biology and a variety of animal models. This is the first study to demonstrate the effects of androgen on hepatic cholesterol by upregulating CYP7A1 gene expression, and will provides a new idea for the molecular mechanism of androgen regulation of lipid metabolism, looking for potential drug targets.

高胆固醇血症是脑卒中、冠心病、心肌梗死、心脏猝死独立而重要的危险因素。近年研究表明，男性雄激素水平降低后，除可导致体力及性欲下降外，更是导致脂代谢紊乱的独立危险因素。我们以C57雄性小鼠行睾丸切除术（ORX）为动物模型，发现ORX 组小鼠肝脏脂肪沉积明显，胆固醇含量增多，胆汁酸水平降低，且胆固醇7α-羟化酶基因（CYP7A1）表达下调。体外试验证实：睾酮可促进CYP7A1基因的表达，而加用雄激素受体拮抗剂这一作用则消失。故我们提出假设：雄激素可通过与其受体结合，促进 CYP7A1基因的表达，加快胆固醇向胆汁酸转化，改善高胆固醇血症。本课题将在现有发现的基础上，进一步运用分子生物学以及多种动物模型，明确雄激素促进CYP7A1基因表达的具体机制。本研究将首次阐述雄激素通过CYP7A1基因调控肝脏胆固醇-胆汁酸代谢，为揭示雄激素调节脂代谢的分子机制提供了新的思路，以寻找潜在的药物靶点。

高胆固醇血症是脑卒中、冠心病、心肌梗死、心脏猝死独立而重要的危险因素。近年研究表明，男性雄激素水平降低后，除可导致体力及性欲下降外，更是导致脂代谢紊乱的独立危险因素。我们以C57小鼠行睾丸切除术（ORX）为动物模型，发现ORX 组小鼠肝脏脂肪沉积明显，胆固醇含量增多，胆汁酸水平降低，且胆汁酸合成限速酶的编码基因--CYP7A1基因表达下调，体外试验证实：在睾酮2nM浓度下可促进CYP7A1基因的表达，而加用雄激素受体拮抗剂这一作用则消失；在睾酮2nM浓度下，胆汁酸BA 的水平升高，使用拮抗剂AR后，胆汁酸BA降低；进一步明确其具体的调控机制发现：利用报告基因系统，与对照组相比，睾酮处理后CYP7A1的表达量增加，同时使用AR拮抗剂后，CYP7A1的表达量降低。通过软件预测，发现CYP7A1基因启动子存在可与雄激素反应元件（ARE）区域相结合的三个结合位点。通过构建不同长度的CYP7A1基因启动子荧光素酶报告基因的质粒，检测该报告基因的荧光素酶活性，与CYP7A1启动子野生型载体（野生型）相比，CYP7A1启动子的727bp - 741bp位点突变型（突变2）应是睾酮经AR对CYP7A1启动子区调控最明显的位点，与之前的预测位点相符。该研究有助于阐明雄激素对于肝脏胆固醇代谢的具体调控机制，为揭示雄激素调节脂代谢的分子机制提供了新的思路；并有望为肝脏胆固醇-胆汁酸代谢的调节提供重要补充，寻找治疗脂代谢异常疾病的潜在药物靶点。