IQGAP1在血管紧张素Ⅱ诱导足细胞凋亡中的作用及其机制探讨

Role of IQGAPI in mediating angiotensin II -induced apoptosis of podocytes and its underlying mechanism

目的研究IQ结构域GTP酶活化蛋白1（IQdomainGTPase-activatingprotein1，IQGAPl）在血管紧张素Ⅱ（Angll）诱导足细胞凋亡中的作用以及可能的分子机制。方法体外培养条件永生性小鼠足细胞（MPC），以不同浓度（0、10-12、10-10、10-8、10-6mol／L）AngⅡ处理MPC或10-8mol／LAngII刺激不同时间（0、1、3、6、12、24h），采用流式细胞术检测细胞凋亡率，免疫荧光、Western印迹法检测IQGAPl的表达及分布。IQGAPlsiRNA转染以及丝裂原活化蛋白激酶（MAPK）通路（包含p38、JNK和ERK1／23条主要通路）抑制剂SB202190（10μmol／L）、SP600125（25μmol／L）或U0126（10μmol／L）预处理MPC后，分别检测MAPK信号蛋白磷酸化水平及细胞凋亡率，并采用免疫共沉淀法研究IQGAPl与ERKl／2结合水平的变化。结果（1）AngⅡ可以诱导足细胞凋亡，且凋亡率随着刺激时间和刺激浓度的增加而进一步增加。（2）正常足细胞IQGAPl主要分布于细胞膜和胞质，随AngⅡ刺激浓度和刺激时间的增加，胞膜和胞质IQGAPl表达逐渐增高，且随剂量和时间增高。（3）SB202190、SP600125或U0126分别预处理足细胞，可显著降低Ang11诱导的足细胞凋亡（P〈0．05），但不影响IQGAPl蛋白表达。（4）IQGAPlsiRNA转染足细胞显著下调ERKl／2磷酸化水平（P〈0．05），降低IQGAPl与ERKl／2结合量（P〈0．05），并抑制AnglI诱导的细胞凋亡（P〈0．05），但对于p38以及JNK通路无显著影响。结论IQGAPl通过ERKl／2MAPK信号通路介导AngⅡ诱导的足细胞凋亡。

Objective To investigate the role of IQ domain GTPase- activating protein 1 （IQGAP1） in angiotensin II （AngII） -induced podocyte apoptosis and the underlying mechanism. Methods Differentiated mouse podocytes were exposed to Ang II at different concentrations for 6 h or at 10-6 mol/L for variable incubation time. Podocyte apoptosis was assessed by flow cytometry. Expression of IQGAP1 was analyzed by immunofluorescence and Western blotting. IQGAP1 siRNA and MAPK pathway inhibitors（10 Ixmol/L SB202190, 25 Ixmol/L SP600125, 10 Ixmol/L U0126） were further introduced to investigate the role of IQGAP1 and MAPK signalings in the process. And co- immunoprecipitation was used to evaluate the interaction between ERK1/2 and IQGAP1. Results （1） Ang II promoted podocyte apoptosis in a dose- and time-dependent manner. （2） IQGAP1 was located in celluar membrane and cytoplasm of cultured podocytes. Exposure to Ang 11 stimulated IQGAP1 expression in a dose- and time- dependent manner, and elevated phosphorylation of p38, JNK, and ERK1/2 simultaneously. （3） Pretreatment with SB202190, SP600125, or U0126 dramatically prevented Ang II -promoted podocyte apoptosis respectively （P 〈 0.05）. However, the protein level of IQGAP1 was not altered. （4） Knockdown of IQGAP1 with siRNA obviously prevented Aug II -induced apoptosis of podocytes（P 〈 0.05） and reduced Aug II -induced phosphorylation of ERK1/2（P 〈 0.05）, but not that of p38, JNK. This was accompanied by a reduced interaction between ERKI/2 and IQGAPI（P 〈 0.05）. Conclusion IQGAP1 contributes to Ang II -induced podocyte apoptosis by interacting with the ERK1/2 signaling protein.