Structure and Function of Integrins in the Kidney

摘要 Tetraspanin CD151与足细胞整合素α3β1的化学计量顺式结合是稳定所必需的 α3β1的活性配体结合构象，从而维持肾小球滤过屏障的完整性 (GFB)。其他研究还表明，炎症介质、生长因子等激活足细胞中的αvβ3 或者，机械/剪切应力在破坏GFB中起着关键作用。综合来看，这些数据表明 α-3-β-1和α-v-β-3在调节GFB动态平衡中起着相反的作用，但其生化和结构基础 这种功能拮抗在疾病中是未知的，以及肾小球如何对完整的损伤做出反应。 足细胞αvβ3缺失或失活仍有待澄清。在初步研究中，我们证明了α与β3 胞外结构域与CD151结合的EC50类似于α3β1，这种相互作用需要αvβ3的活性构象 并被先前研究中用作部分激动剂的αvβ3抑制剂促进。这些数据让我们了解到 提出并验证这样一种假设，即在疾病状态下激活αvβ3会使CD151脱离结合 到α3β1，从而损害最佳的α3β1功能并扰乱GFB。在其他初步研究中，我们 证明在复合体中获得非活性构象整合素的低温EM结构的可行性 为确定活性整合素构象的结构基础提供了可行性 这与CD151形成了复合体。我们还产生了足细胞特异性缺失αv和 开发了一类新的αvβ3抑制剂，这种抑制剂不是部分激动剂，可以预防而不是促进 αvβ3/CD151的相关性，这也将使我们能够检查当αvβ3 在蛋白尿性肾病的啮齿动物模型中，基因或药物失活。

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.