Roscher Anne, Hasegawa Tomoka, Dohnke Sebastian, Ocaña-Morgner Carlos, Amizuka Norio, Jessberger Rolf, Garbe Annette I
Institute of Physiological Chemistry, Technische Universität Dresden, Germany.
Department of Developmental Biology of Hard Tissue, Graduate School of Dental Medicine, Hokkaido University, Sapporo, Japan.
Bone Rep. 2016 Jul 19;5:214-221. doi: 10.1016/j.bonr.2016.07.002. eCollection 2016 Dec.
Osteoclasts are bone resorbing cells acting as key mediators of bone disorders. Upon adhesion to bone, osteoclasts polarize and reorganize their cytoskeleton to generate a ring-like F-actin-rich structure, the sealing zone, wherein the osteoclast's resorptive organelle, the ruffled border, is formed. The dynamic self-organization of actin-rich adhesive structures, the podosomes, from clusters to belts is crucial for osteoclast-mediated bone degradation. Mice lacking the protein SWAP-70 display an osteopetrotic phenotype due to defective bone resorption caused by impaired actin ring formation in osteoclasts. To further elucidate the mechanisms underlying this defect, we investigated the specific function of SWAP-70 in the organization and dynamics of podosomes. These detailed studies show that the transition from podosome clusters to rings is impaired in osteoclasts. Live cell imaging of dynamic F-actin turnover and SWAP-70 localization during podosome patterning indicate that SWAP-70 is dispensable for cluster formation but plays a key role in F-actin ring generation. Our data provide insights in the role of SWAP-70's F-actin binding domain and pleckstrin homology (PH) domain in the proper localization of SWAP-70 and formation of a peripheral podosome belt, respectively. bone analyses revealed that SWAP-70-deficient osteoclasts exhibit defective ruffled border formation and V-ATPase expression. Our findings suggest an important role of membrane binding of SWAP-70 for the regulation of actin dynamics, which is essential for podosome patterning, and thus for the resorptive activity of osteoclasts.
破骨细胞是骨吸收细胞，是骨疾病的关键介质。在黏附于骨后，破骨细胞极化并重新组织其细胞骨架，以形成富含丝状肌动蛋白（F-肌动蛋白）的环状结构，即封闭区，破骨细胞的吸收细胞器——皱褶缘在其中形成。富含肌动蛋白的黏附结构——足体，从簇状到带状的动态自组织对于破骨细胞介导的骨降解至关重要。缺乏蛋白质SWAP-70的小鼠表现出骨石化表型，这是由于破骨细胞中肌动蛋白环形成受损导致骨吸收缺陷所致。为了进一步阐明这种缺陷背后的机制，我们研究了SWAP-70在足体组织和动态变化中的具体功能。这些详细研究表明，破骨细胞中从足体簇到环的转变受损。在足体形成过程中对动态F-肌动蛋白周转和SWAP-70定位进行的活细胞成像表明，SWAP-70对于簇的形成并非必需，但在F-肌动蛋白环的生成中起关键作用。我们的数据揭示了SWAP-70的F-肌动蛋白结合结构域和普列克底物蛋白同源（PH）结构域分别在SWAP-70正确定位和外周足体带形成中的作用。骨分析显示，缺乏SWAP-70的破骨细胞表现出皱褶缘形成缺陷和V-ATP酶表达缺陷。我们的研究结果表明，SWAP-70的膜结合对于肌动蛋白动力学的调节具有重要作用，而肌动蛋白动力学对于足体形成至关重要，因此对于破骨细胞的吸收活性也至关重要。
