新G蛋白偶联受体GPP142调控胆固醇代谢的作用及机制

Hypercholesterolemia, which is critically increasing the burden of cardiovascular diseases, has been growing into a major epidemic both in the west and in China. In the past two years, during the research of G protein-coupled receptors which contributed almost 40% of targeted interventions of modern drug development, a new member GPR142 has been found to be involved in insulin secretion and glucose lowering. But little is known for its effect in population study or lipid metabolism. Using the data in a small sample of obese population, our team found that the GPR142 R267W variant was significantly associated with serum cholesterol levels and the association was validated in a cohort study of 10,000 community-based participants. We then constructed GPR142 wild-type and R267W site-mutated plasmids and demonstrated that this was a functionally inactive mutation. More surprisingly, the expression of genes related to cholesterol synthesis was significantly inhibited in the hepatocytes transfected with wild-type plasmids, while the inhibitory effect was weakened in the hepatocytes transfected mutant plasmids. In addition, high cholesterol diet feeding resulted in a significant reduction of GPR142 expression in mouse livers. Accordingly, we speculate that GPR142 is involved in the regulation of liver cholesterol synthesis. And we will take a further step to carry out animal and molecular biological research to confirm the key role of GPR142 in regulating cholesterol synthesis and to elucidate its specific mechanism. The causal association between GPR142 mutation and serum cholesterol abnormalities will be also verified through longitudinal population study. Our work will surely provide a further understanding of the pathogenesis of hypercholesterolemia and the development of its drug targets.

高胆固醇血症是导致心血管疾病的重要原因。近年研究提示新的G蛋白偶联受体GPR142参与胰岛素分泌与血糖调控，但缺乏血脂代谢相关研究。申请人团队在肥胖人群研究中发现GPR142的R267W位点突变与血清胆固醇水平显著相关，进一步构建GPR142野生型与点突变质粒，并证实其为功能失活突变；深入研究还揭示转染野生型质粒的肝细胞内，胆固醇合成基因表达被抑制，而在转染突变质粒组抑制效应减弱;高胆固醇饲料喂养可致小鼠肝组织的GPR142表达显著减少。据此，申请人团队认为GPR142参与了调控肝脏的胆固醇合成。本课题拟在前期研究基础上深入研究，进一步证实GPR142调控胆固醇合成的关键作用及具体机制，并通过人群随访研究证明GPR142突变与血清胆固醇异常的因果关联。研究结果将为深入阐明高胆固醇血症的发病机制及揭示新的药物靶点开发提供科学依据。

心血管疾病的流行已成为全球性的重大公共卫生问题。心血管疾病的原因众多，高胆固醇血症、高血压、向心性肥胖、糖尿病等代谢性疾病是最常见的诱因；其中，高胆固醇血症尤为重要。我们首先利用小样本的GOCY队列的DNA样本库，进行了全外显子组测序。结合文献报道，我们重点研究了GPR142错义突变位点，通过生物信息学分析及评估，我们将关注点集中在一个低频GPR142错义变异位点（c.799 C>G, p.R267W ）（rs117073661）上，其碱基变化导致了第267位的精氨酸（R）突变成了色氨酸（W），即R267W。在肥胖组发现14例，而在对照组仅有7例，虽未达到统计学差异，但是有富集于肥胖病例组趋势（P =0.133）。于是，借助这一线索，我们后续开展了更大样本的宝山社区自然人群队列的临床和遗传资料分析工作，进行深入探索。通过遗传变异位点和临床资料进行关联分析发现，虽然GPR142的R267W突变和人群的肥胖程度相关性并不明显，但其与血清胆固醇水平显著相关。进一步在大样本的宝山队列人群中进行多元线性回归分析，经校正年龄、性别、生活方式和血糖、血压等其他代谢指标等混杂因素后，R267W突变和胆固醇水平具有独立的相关性，R267W位点每增加一个风险等位基因（G-allele），血清总胆固醇水平增加0.24±0.07 mmol/l（P =0.0006）。在基础研究中，R267W突变导致GPR142膜受体蛋白的膜定位功能受损。在HepG2细胞上过表达GPR142或者加入GPR142的天然配体L-色氨酸，可以显著抑制胆固醇合成关键基因的表达。通过在高胆固醇饮食小鼠饲料中添加L-色氨酸，小鼠的血浆低密度脂蛋白胆固醇（LDL-c）显著降低，而高密度脂蛋白胆固醇（HDL-c）有增高趋势。我们的研究提示GPR142基因参与机体的胆固醇代谢调节，并有望成为新的降脂干预靶点。