SLC4A2-mediated Cl-/HCO3- exchange activity is essential for calpain-dependent regulation of the actin cytoskeleton in osteoclasts
SLC4A2-mediated Cl-/HCO3- exchange activity is essential for calpain-dependent regulation of the actin cytoskeleton in osteoclasts
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DOI：
10.1073/pnas.1206392110
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发表时间：
2013-02-05
影响因子：
11.1
通讯作者：
Aliprantis, Antonios O.
中科院分区：
文献类型：
--
作者：
Coury, Fabienne;Zenger, Serhan;Aliprantis, Antonios O.
骨重塑需要破骨细胞在顶膜和骨表面之间产生并维持酸化的吸收室，以溶解骨基质内的羟基磷灰石晶体。该酸化过程需要（i）液泡H+-ATP酶分泌顶端质子，（ii）肌动蛋白细胞骨架重组为足体带，形成垫圈以限制腔隙酸泄漏，以及（iii）阴离子交换剂吸收基底外侧氯离子并排出碳酸氢根，为顶端酸分泌提供Cl-许可，同时防止细胞质碱化。在这里，我们发现破骨细胞靶向缺失溶质载体家族 4 阴离子交换剂成员 2 (Slc4a2) 的小鼠会导致骨硬化症。我们进一步证明了破骨细胞中 SLC4A2 功能丧失的一个先前未被认识的后果：钙蛋白酶依赖性足体分解失调，导致异常肌动蛋白带形成、细胞扩散和迁移。用功能明确的 SLC4A2 突变体拯救 SLC4A2 缺陷的破骨细胞表明，阴离子交换活性和细胞内 pH 值对肌动蛋白细胞骨架重组的调节，与 SLC4A2 的长 N 端胞质结构域无关。这些数据表明，通过阴离子交换维持破骨细胞内的 pH 值可调节骨吸收所需的肌动蛋白上层结构。
Bone remodeling requires osteoclasts to generate and maintain an acidified resorption compartment between the apical membrane and the bone surface to solubilize hydroxyapatite crystals within the bone matrix. This acidification process requires (i) apical proton secretion by a vacuolar H+-ATPase, (ii) actin cytoskeleton reorganization into a podosome belt that forms a gasket to restrict lacunar acid leakage, and (iii) basolateral chloride uptake and bicarbonate extrusion by an anion exchanger to provide Cl-permissive for apical acid secretion while preventing cytoplasmic alkalinization. Here we show that osteoclast-targeted deletion in mice of solute carrier family 4 anion exchanger member 2 (Slc4a2) results in osteopetrosis. We further demonstrate a previously unrecognized consequence of SLC4A2 loss of function in the osteoclast: dysregulation of calpain-dependent podosome disassembly, leading to abnormal actin belt formation, cell spreading, and migration. Rescue of SLC4A2-deficient osteoclasts with functionally defined mutants of SLC4A2 indicates regulation of actin cytoskeletal reorganization by anion-exchange activity and intracellular pH, independent of SLC4A2's long N-terminal cytoplasmic domain. These data suggest that maintenance of intracellular pH in osteoclasts through anion exchange regulates the actin superstructures required for bone resorption.