CRP对脂联素基因表达和分泌的影响及其调控机制研究

Adiponectin, the most abundant protein secreted by white adipose tissue, is known for its involvement in obesity-related disorders such as insulin resistance, type 2 diabetes mellitus and atherosclerosis. Besides its well-known antidiabetic and antiatherosclerotic properties, accumulating evidence suggests that adiponectin may also have anticancer properties and be cardioprotective. It has been suggested that pharmacological strategies aimed at augmenting adiponectin levels or action may generate novel drugs to treat related diseases. However, the use of adiponectin as therapeutic targets is complicated by the presence of different adiponectin oligomeric isoforms. C-reactive protein (CRP) is one of the most sensitive inflammatory markers. Our group and others have reported that serum hs-CRP is inversely related to serum adiponectin in certain defined subjects. In our previous study, we found that the expression of CRP in liver and adipose tissues of insulin resistant rats induced by high fat diet(HFD) was increased, and adiponectin mRNA in adipose tissue was decreased. Northern and western blot analysis revealed that CRP-treatment inhibited adiponectin mRNA expression and secretion in a dose- and time-dependent manner in 3T3-L1 adipocytes. A recent study showed that human CRP overexpression facilitated the development of insulin resistance and hepatosteatosis with HFD in association with adiponectin down-regulation. Based on the findings mentioned above,It showed that the elevation of CRP level may lead to insulin resistance and artherosclerosis via inhibiting the expression and secretion of adiponectin. In the present study, we aim to investgate the molecular mechanism of CRP regulating adiponectin gene expression and secretion. Focusing on the upstream regulation of adiponectin by CRP may offer an elegant and novel therapeutic strategy that circumvents problems in designing drugs to mimic the complex higher order structure of adiponectin.

脂联素是白色脂肪组织中表达最丰富的细胞因子，在体内以三聚体、六聚体和高分子量多聚体等结构形式存在，具有抗糖尿病、抗动脉粥样硬化、抗肿瘤及保护心脏的作用。近年来研究表明CRP不仅仅是炎性标志物，它还是体内具有生物活性的炎症因子。我们前期研究发现，在胰岛素抵抗大鼠及人群，CRP表达增加，脂联素表达下降；在3T3-L1脂肪细胞，Northern、Western blot结果显示CRP以时间、剂量依赖方式抑制脂联素的表达和分泌；国外最新研究发现CRP转基因小鼠脂联素表达下降；以上研究结果表明CRP可能调控脂联素的表达和分泌。本项目拟进一步在细胞和整体水平观察CRP对脂联素表达和分泌的影响，并从信号途径入手，探明CRP直接调控脂联素表达和分泌的分子机制。本研究具有源头创新性，加强对脂联素基因表达调控的研究，有望绕开模拟脂联素复杂的高级结构的难题，找到一种新颖的药物以提高内源性脂联素浓度，对2型糖尿病、动脉粥样硬化、肿瘤等疾病的防治提供帮助。

脂联素具有改善胰岛素抵抗、抗糖尿病、抗动脉粥样硬化的作用，在体内以三聚体、六聚体和高分子量多聚体等结构形式存在。加强对脂联素基因表达调控的研究，有望绕开模拟脂联素复杂的高级结构的难题，找到一种新颖的药物以提高内源性脂联素浓度，对2型糖尿病、动脉粥样硬化等疾病的防治提供帮助。本项目观察了CRP对脂联素表达和分泌的影响，并探讨了其作用机制。研究发现，25µg/mlCRP作用24小时即显著抑制脂联素的表达和分泌，其分别下降了31%及19%；50µg/ml CRP 则使脂联素的表达、分泌分别下降了52%及41%；Realtime PCR结果显示，PI-3K的两种抑制剂10µM LY294002、100 nM wortmannin均部分逆转了CRP对脂联素的抑制作用，提示CRP可能通过PI-3K途径影响脂联素的表达；此外，我们构建了含1.1kb脂联素启动子的PGL3质粒，用之转染诱导成熟的3T3-L1脂肪细胞，结果显示，CRP不影响荧光素酶的表达，表明CRP影响脂联素表达的转录调控区可能在这1.1kb以外，或可能是通过影响脂联素mRNA的稳定性起作用的。研究还发现，CRP可能还通过促进TNF-α的表达、抑制PPARγ基因的表达影响脂联素的表达和分泌。 在HepG2细胞，我们用Realtime PCR方法发现：脂联素以剂量依赖方式抑制IL-6引起的CRP表达的上升作用。脂联素、CRP、胰岛素抵抗之间的相互关系表明：CRP水平增高会引起脂联素水平下降，导致胰岛素抵抗的发生；同时低脂联素血症又会造成血CRP水平更高，从而形成一种恶性循环，进一步加重胰岛素抵抗等疾病。.本课题组成员已撰写并发表论文13篇(标注基金号），其中SCI收录4篇。已录用论文3篇（已附录用证明），研究生毕业论文1篇。研究成果对2型糖尿病、动脉粥样硬化等疾病的防治具有重要意义。