黄芩素靶向Cdx2-PXR通路抗溃疡性结肠炎的作用机制研究

Ulcerative colitis (UC ) has become the most popular disease occurred in bowel and the key factor that causes chronic diarrhea.Up to now, there is no effective and ideal clinical drugs in the treatment of UC. It is suggested that pregnane x receptor (PXR) could be a drug target for the treatment of UC. Investigation on PXR ligands/agonists is suggested to be crucial for the novel therapeutic drug discovery with respect to the cure of UC in the future. Hence,to find out PXR ligands/agonists from natural medicines with well defined effects in the treatment of UC has attracted much interests. Pregnane x receptor (PXR) is a master gene overseeing detoxification of wide number of xenobiotics and is critical for maintenance on the intestinal integrity. It is a regulator of NFκB gene through binding to the promoter area and up-regulating gene expression of the latter. NFκB is well defined as a main coordinator in inflammatory reactions and the central manipulator for the expression of the proinflammatory cytokines, such as TNFα,IL-1, IL-6 etc. In recent years, much interests have been concentrated on the further disclosure of the effect of inflammatory reactive chain PXR-NFκB-COX2-TNFα via which PXR ligands/agonists presents the protection against UC. In our recent studies, we found baicalein could alleviate gut inflammation by acting as a gut specific agonist of PXR and through the manner of modulating PXR-NFκB-COX2-TNFα pathway. Baicalein in the meantime could up-regulate the gene expression of PXR. In our earlier studies, it was indicated that the transcription factor Cdx2 (caudal-related homeobox protein 2) as a novel modulator involving in the maintaining the gut immunity homeostasis, could bind to the promoter region and drive the gene transcription of PXR. We found Cdx2 could up-regulate the gene expression of PXR as well. The most intriguing is that preliminary experiments showed that baicalein could up-regulate the expression of Cdx2 gene in both mRNA and protein levels. Hence, the hypothesis is deduced that the pathway PXR-NFκB-COX2-TNFα through which baicalein exerts the protection from ulcerative colitis may be modulated by Cdx2, and the signaling reactive chain behind baicalein's anti-colitis effect may be extended to Cdx2-PXR-NFκB-COX2-TNFα. Up to now it is still unrevealed with respect to Cdx2 mediated PXR agonist's protection mechanism towards gut inflammation. In the present study, Cdx2-PXR regulation mechanism behind baicalein's anti-colitis effect will be well identified and validated through an array of assays, such as gene reportor, gene knock-dowm, gene blockage, protein blockage, gene overexpression, etc. and through a precise investigation towards chemical colitis mice.The present study will provide a novel pharmacological mechanism associated to PXR agonists in the protection from ulcerative colitis.

近年孕烷x受体（PXR）激动剂通过PXR-NFκB-COX2-TNFα途径抗UC作用成为国际研究热点。项目组前期研究中，首次发现黄芩素是PXR的组织（小肠、直肠和结肠）特异性激动剂并通过以上信号通路起到UC防治作用。过去我们曾发现异型盒蛋白2（Cdx2）是PXR的上游调控转录因子并参与维持肠道免疫动态平衡。而前期预实验发现，黄芩素可以剂量依赖性上调Cdx2表达。我们推测Cdx2-PXR信号传导可能是黄芩素防治UC作用信号链的上游调控机制。而有关PXR激动剂通过Cdx2-PXR信号机制抗UC作用研究，迄今国内外尚无报道。我们拟建立基于基因沉默和蛋白阻遏细胞信号传导、炎症信号分子调控及UC病理、生理指标的关联分析方法，运用基因汇报、敲除、抑制剂、超表达、阻断剂、UC模型等手段，在前期研究基础上，进一步阐明黄芩素通过Cdx2-PXR信号途径防治UC的分子机理，为PXR激动剂UC防治机制提供新理论

本项目运用药理学、药效学、分子细胞生物学等技术，建立基于基因沉默和蛋白阻遏细胞信号传导、炎症信号分子调控及UC病理、生理指标的关联分析方法，结合实验性UC小鼠的病理、生理指标，对黄芩素抗UC作用和机制进行研究。研究结果表明，黄芩素能够减轻UC小鼠模型的结肠黏膜病理损伤症状，减轻炎性细胞浸润，对UC小鼠模型具有保护作用；进一步药理研究表明，黄芩素是PXR受体激动剂，通过上调CDX2表达，间接激活PXR基因，抑制下游炎症信号通路基因的表达，从而减轻UC小鼠模型的病理损伤症状。本项目为PXR激动剂的UC防治机制提供新理论和药物作用新靶标。