Blaschke Florian, Takata Yasunori, Caglayan Evren, Collins Alan, Tontonoz Peter, Hsueh Willa A, Tangirala Rajendra K
Division of Endocrinology, Diabetes and Hypertension, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA.
Circ Res. 2006 Dec 8;99(12):e88-99. doi: 10.1161/01.RES.0000252878.34269.06. Epub 2006 Nov 16.
C-reactive protein (CRP), the prototypical human acute phase protein, is an independent risk predictor of future cardiovascular events, both in healthy individuals and in patients with known cardiovascular disease. In addition, previous studies indicate that CRP might have direct proatherogenic properties. Ligand activation of the liver X receptor (LXR), a member of the nuclear hormone receptor superfamily, inhibits inflammatory gene expression in macrophages and attenuates the development of atherosclerosis in various animal models. We demonstrate herein that 2 synthetic LXR ligands, T0901317 and GW3965, inhibit interleukin-1beta/interleukin-6-induced CRP mRNA and protein expression in human hepatocytes. Knockdown of LXRalpha/beta by short interfering RNAs completely abolished the inhibitory effect of the LXR agonist T0901317 on cytokine-induced CRP gene transcription. Transient transfection experiments with 5'-deletion CRP promoter constructs identified a region from -125 to -256 relative to the initiation site that mediated the inhibitory effect of LXR ligands on CRP gene transcription. Depletion of the nuclear receptor corepressor by specific short interfering RNA increased cytokine-inducible CRP mRNA expression and promoter activity and reversed LXR ligand-mediated repression of CRP gene transcription. Chromatin immunoprecipitation assays indicated that nuclear receptor corepressor is present on the endogenous CRP promoter under basal conditions. Cytokine-induced clearance of nuclear receptor corepressor complexes was inhibited by LXR ligand treatment, maintaining the CRP gene in a repressed state. Finally, treatment of C57Bl6/J mice with LXR ligands attenuated lipopolysaccharide-induced mouse CRP and serum amyloid P component gene expression in the liver, whereas no effect was observed in LXRalphabeta knockout mice. Our observations identify a novel mechanism of inflammatory gene regulation by LXR ligands. Thus, inhibition of CRP expression by LXR agonists may provide a promising approach to impact initiation and progression of atherosclerosis.
C反应蛋白（CRP）作为典型的人类急性期蛋白，无论是在健康个体还是已知患有心血管疾病的患者中，都是未来心血管事件的独立风险预测因子。此外，先前的研究表明CRP可能具有直接的促动脉粥样硬化特性。肝脏X受体（LXR）是核激素受体超家族的成员，其配体激活可抑制巨噬细胞中炎症基因的表达，并在各种动物模型中减轻动脉粥样硬化的发展。我们在此证明，两种合成的LXR配体T0901317和GW3965可抑制白细胞介素-1β/白细胞介素-6诱导的人肝细胞中CRP mRNA和蛋白的表达。通过短干扰RNA敲低LXRα/β可完全消除LXR激动剂T0901317对细胞因子诱导的CRP基因转录的抑制作用。用5'-缺失CRP启动子构建体进行的瞬时转染实验确定了相对于起始位点从-125至-256的区域，该区域介导了LXR配体对CRP基因转录的抑制作用。通过特异性短干扰RNA消耗核受体共抑制因子可增加细胞因子诱导的CRP mRNA表达和启动子活性，并逆转LXR配体介导的CRP基因转录抑制。染色质免疫沉淀分析表明，在基础条件下，核受体共抑制因子存在于内源性CRP启动子上。LXR配体处理可抑制细胞因子诱导的核受体共抑制因子复合物的清除，使CRP基因保持在抑制状态。最后，用LXR配体处理C57Bl6/J小鼠可减轻脂多糖诱导的小鼠肝脏中CRP和血清淀粉样蛋白P成分基因的表达，而在LXRαβ敲除小鼠中未观察到效果。我们的观察结果确定了LXR配体调节炎症基因的新机制。因此，LXR激动剂抑制CRP表达可能为影响动脉粥样硬化的发生和发展提供一种有前景的方法。
