PI(4,5)P2介导胆固醇调节肾脏集合管上皮细胞ROMK1通道的机制研究

Cyclosporine A(CsA), an immunosuppressant drug which can causes hyperkalemia. However, the machanism remains unclear. As a member of Kir channel superfamily, ROMK1 plays an important role in potassium secretion of distal nephron, suggest that ROMK1 may be involved in CsA induced hyperkalemia. We have validated that CsA can inhibits ROMK1 activity in renal collecting duct epithelial cells which is associated with elevation of membrane cholesterol. Therefore, investigating how cholesterol regulates ROMK1 becomes emphasis. Our preliminary studies suggest that lipid rafts which are rich in cholesterol are mainly located in microvilli, but ROMK1 channels which are anchored in non-lipid rafts are potentially located in planar regions of cell membrane. PI(4,5)P2, a potent ROMK1 channel activator via a direction interaction, is mainly locates in microvilli by binding to the cholesterol in some manner. So, we suppose that cholesterol may indirectly regulate ROMK1 channel by modulating PI(4,5)P2 distribution between microvilli and planar region in the cell membrane. We will use mouse collecting duct epithelial cells combined with a variety of experimental methods, especially with scanning ion conductance microscopy (SICM) microstructure navigation patch- clamp technique to illuminate the pathway of ROMK1 regulation by cholesterol-dependent distribution of PI(4,5)P2. This research will firstly establish the dynamic model for lipid-protein distribution, transfer and interaction among the microstructures of cell membrane; and reveal the machanism of hyperkalemia induced by CsA and lipid metabolism disorders, provide potential targets for clinical prevention and treatment.

免疫抑制剂环孢霉素A（CsA）可诱发高钾血症，机制尚未阐明，ROMK1作为远端肾单位主要泌钾通道可能参与其中。我们已证实CsA可抑制ROMK1活性且与上调细胞膜胆固醇有关，所以探究胆固醇对ROMK1的调节机制成为重点。预实验中发现富含胆固醇的脂质筏主要位于细胞膜微绒毛中，而ROMK1在非脂质筏内可能位于细胞膜平面区域，膜脂质-PI(4,5)P2是ROMK1的直接激活剂，却常和胆固醇绑定，因此推测胆固醇调节ROMK1活性是通过改变PI(4,5)P2在微绒毛及平面区域的分布间接实现的。我们将应用鼠集合管上皮细胞作为研究对象，结合多种实验手段并通过离子电导显微镜（SICM）的微结构定位膜片钳技术阐明PI(4,5)P2的胆固醇依赖性分布对ROMK1的调节途径。本课题将首次建立脂质-蛋白在膜微结构间的分布，转移及相互作用的新动态模型；揭示CsA及脂质代谢紊乱引起的高钾血症机制，为临床防治提供靶点 。

免疫抑制剂-环孢霉素A（CsA）可诱发高钾血症，机制尚未阐明。我们之前的研究证明洛伐他汀可通过降低细胞内胆固醇的合成逆转CsA导致的肾集合管(CCD)上皮细胞损伤；既往在细胞表达模型及人工细胞膜上的研究证实外源性胆固醇可直接抑制内向整流钾通道，包括ROMK1（Kir1.1）,作为Kir超家族一员，对远端肾单位泌钾起重要作用。因此我们推测洛伐他汀可能通过降低CCD细胞内胆固醇合成激活ROMK1通道，从而研究胆固醇对ROMK1的调节机制成为本课题的重点。Western-blots实验显示鼠集合管上皮细胞（mpkCCDc14）上ROMK1确定表达且分子量与分离的鼠集合管上表达一致，而且通过DTT分解发现ROMK1在细胞膜上多以二聚体存在。共聚焦实验显示富含胆固醇的脂质筏主要位于细胞膜微绒毛上，而ROMK1在非脂质筏内位于细胞膜平面区域；而ROMK1直接激活因子PIP2及其合成前体PI(4)P5K受胆固醇调节在静息状态下主要位于微绒毛上，因此可以解释为什么ROMK1基础活性很低。进一步实验发现洛伐他汀可通过降低膜胆固醇水平使PI(4)P5K释放到平面区域生成PIP2增加ROMK1活性；而在静息状态下外源性增加胆固醇对ROMK1活性无影响。本课题首次建立脂质-蛋白在膜微结构间的分布，转移及相互作用的动态模型；揭示CsA及脂质代谢紊乱通过胆固醇介导引起高钾血症机制，为临床防治提供靶点，他汀类药物可能作为解决这一临床难题的潜在治疗方法。