Max Planck Institute of Biochemistry, D-82152 Martinsried, Germany.
J Cell Biol. 2011 Mar 7;192(5):883-97. doi: 10.1083/jcb.201007141. Epub 2011 Feb 28.
The blood cell-specific kindlin-3 protein is required to activate leukocyte and platelet integrins. In line with this function, mutations in the KINDLIN-3 gene in man cause immunodeficiency and severe bleeding. Some patients also suffer from osteopetrosis, but the underlying mechanism leading to abnormal bone turnover is unknown. Here we show that kindlin-3-deficient mice develop severe osteopetrosis because of profound adhesion and spreading defects in bone-resorbing osteoclasts. Mechanistically, loss of kindlin-3 impairs the activation of β1, β2, and β3 integrin classes expressed on osteoclasts, which in turn abrogates the formation of podosomes and sealing zones required for bone resorption. In agreement with these findings, genetic ablation of all integrin classes abolishes the development of podosomes, mimicking kindlin-3 deficiency. Although loss of single integrin classes gives rise to podosomes, their resorptive activity is impaired. These findings show that osteoclasts require their entire integrin repertoire to be regulated by kindlin-3 to orchestrate bone homeostasis.
血细胞质特异性凝溶胶蛋白激酶 3（kindlin-3）蛋白对于激活白细胞和血小板整合素是必需的。与该功能一致，人类 KINDLIN-3 基因的突变会导致免疫缺陷和严重出血。一些患者还患有骨质石化症，但导致异常骨转换的潜在机制尚不清楚。在这里，我们发现缺乏凝溶胶蛋白激酶 3 的小鼠由于破骨细胞中严重的黏附和扩散缺陷而发展为严重的骨质石化症。从机制上讲，凝溶胶蛋白激酶 3 的缺失会损害破骨细胞上表达的β1、β2 和β3 整联蛋白类的激活，进而破坏破骨细胞进行骨吸收所需的足突和封闭区的形成。与这些发现一致的是，所有整联蛋白类的遗传缺失会导致足突的形成，模拟凝溶胶蛋白激酶 3 的缺失。尽管单个整联蛋白类的缺失会导致足突的形成，但它们的吸收活性会受到损害。这些发现表明，破骨细胞需要其整个整联蛋白组来被凝溶胶蛋白激酶 3 调节，以协调骨稳态。
