苦物质及其受体T2R介导呼吸道平滑肌松弛的机制研究

除感知味觉外，苦味受体（T2R）信号系统可高效松弛呼吸道平滑肌（ASM），可能是新一代哮喘类等药物的靶点，但其信号通路还不清楚。前期研究发现：苦物质虽引起ASM低钙释放，但可高效阻止乙酰胆碱（ACh）刺激ASM收缩时的高钙释放，首先发现苦物质是通过封闭钙信号完成舒张效应的；T2R偶联小G蛋白Gαt（由Gnats编码）是介导钙信号封闭的必需分子，提示T2R／AChR两个信号系统间的相互作用是苦物质松弛效应的关键机制。通过比较Gαt与Gq 的结构特征，我们提出苦物质的松弛机制可能是：T2R激活后，释放出Gαt与AChR进行跨受体偶联，通过竞争抑制Gq与AChR的偶联循环、阻止PLCβ／IP3介导的高钙释放，完成收缩“刹车”。为证实该观点，我们将利用Gnats多基因敲除小鼠、通过生理、生化学等方法系统阐明T2R／AChR信号间的相互作用及其调节途径，提出一个苦物质松弛平滑肌的新机制。

In addition to sense taste, bitter taste receptor T2R signal cascade can mediate an efficient relaxation of airway smooth muscle (ASM), which is considered as a critical target of new generation drugs for asthma and the related. However, the regulatory signal scenario for the relaxation has been unclear. Our preliminary observations show that bitter substances can block robust calcium release induced by acetylcholine although it induces a slight calcium release itself. This indicates that the relaxation mediated by bitter substances is accomplished through targeting on calcium release. Moreover, Gαt, a family of small GTPases coupled with T2R that is coded by Gnats genes, is required for blocking calcium release and relaxing ASM, indicating an interplay between T2R and AChR signal cascades that serves as the principle mechanism of the relaxation effect. Together with the structural comparison of Gαt and Gq proteins, we propose a relaxation mechanism of bitter substances stating as: upon activation of T2R by bitter substances, Gαt is uncoupled and the released Gαt cross-binds with AChR thereby competitively inhibiting Gq cycle coupling with AChR. As a consequence, PLCβ/IP3-mediated calcium release necessary for contraction is blocked, and results in contraction braking. To test this proposal, we plan to use Gnats multiple gene KO mice and various physiological and biochemical analysis to uncover the interplay of T2R and AChR signaling cascades and reveal a regulatory scenario of bitter substance-mediated ASM relaxation, which would be critical for new drug development of asthma and its related diseases.