Structure and Function of Integrins in the Kidney

摘要 四跨膜蛋白CD 151与足细胞整合素α3β1的化学计量顺式缔合对于稳定 α3β1处于活性配体结合构象，从而维持肾小球滤过屏障的完整性 （GFB）。其他研究也表明，足细胞中的αvβ3被炎症介质、生长因子 或机械/剪切应力在破坏GFB中起关键作用。综合来看，这些数据表明， α3β1和αvβ3在调节GFB内稳态中起相反的作用，但GFB内稳态的生化和结构基础， 疾病中的这种功能性拮抗作用尚不清楚，肾小球如何对损伤作出反应， 足细胞αvβ3的缺失或失活仍有待澄清。在初步研究中，我们表明αvβ3 胞外域以与α3β1相似的EC 50结合CD 151，这种相互作用需要αvβ3的活性构象 并且通过在先前研究中用作部分激动剂的αvβ3抑制剂来促进。这些数据使我们 提出并检验了一个假设，即在疾病状态下αvβ3的激活会使CD 151与CD 151分离， 转化为α3β1，从而损害最佳α3β1功能并破坏GFB。在其他初步研究中，我们 证明了在复合物中获得无活性构象的整合素的冷冻-EM结构的可行性 与四跨膜蛋白，提供了确定活性整合素构象的结构基础的可行性 与CD 151形成复合物。我们还产生了足细胞特异性缺失αv的小鼠， 开发了一类新型αvβ3抑制剂，不是部分激动剂， αvβ3/CD 151的相关性，这也将使我们能够检查当αvβ3被抑制时肾小球对损伤的反应。 在啮齿类动物蛋白尿肾病模型中，

Abstract The stoichiometric cis association of the tetraspanin CD151 with podocyte integrin α3β1 is essential for stabilizing α3β1 in an active ligand-binding conformation, thus maintaining the integrity of the glomerular filtration barrier (GFB). Other studies also show that activation of αvβ3 in podocytes by inflammatory mediators, growth factors or mechanical/shear stress plays a critical role in disrupting the GFB. Taken together, these data suggest that α3β1 and αvβ3 play opposing roles in regulating GFB homeostasis, but the biochemical and structural basis of this functional antagonism in disease is unknown and how the glomerulus responds to injury in the complete absence or inactivation of podocyte αvβ3 remains to be clarified. In preliminary studies, we show that αvβ3 ectodomain binds CD151 with similar EC50 to α3β1, that this interaction requires the active conformation of αvβ3 and is promoted by the αvβ3 inhibitors used in prior studies acting as partial agonists. These data lead us to propose and test the hypothesis that activation of αvβ3 in disease states sequesters CD151 away from binding to α3β1, thus impairing optimal α3β1 function and disrupting the GFB. In other preliminary studies, we demonstrate the feasibility of obtaining a cryo-EM structure of an integrin in an inactive conformation in complex with a tetraspanin, providing the feasibility for determining the structural basis of the active integrin conformation that forms the complex with CD151. We have also generated mice with podocyte specific deletion of αv and developed a novel class of αvβ3 inhibitors that are not partial agonists and that prevent rather than promote αvβ3/CD151 association, which will also allow us to examine the glomerular response to injury when αvβ3 is inactivated genetically or pharmacologically in rodent models of proteinuric kidney disease.