Talbot Julie, Verrecchia Franck
INSERM, UMR 957, Université de Nantes, Laboratoire de Physiopathologie de la Résorption Osseuse et Thérapie des Tumeurs Osseuses Primitives, Faculté de Médecine, CHU de Nantes, Nantes, France.
Biol Aujourdhui. 2012;206(2):125-34. doi: 10.1051/jbio/2012016. Epub 2012 Jul 4.
Gap junctions are specialized plasma membrane structures consisting of transmembrane channels that directly link the cytoplasms of adjoining cells and mediate the reciprocal exchange of ions and low molecular weight molecules (<1200 Da). Structural studies have demonstrated that each gap junctional channel is formed by the extracellular interaction of two hemi-channels (connexons). Each connexon is a hexameric assembly of protein subunits (connexins), which delineate an aqueous pore. Connexins are homologous proteins encoded by a multigene family and are named according to their predicted molecular weight. Connexin 43, widely distributed in different cell types, is the main gap junction protein expressed in human bone cells, although Cx45 and Cx46 have been reported to be expressed as well. Bone remodeling requires coordinated activity among osteoblasts and osteoclasts. Osteoblasts (bone forming cells) are derived from mesenchymal stem cells, and osteoclasts (bone resorbing cells), are multinucleated cells of monocyte/macrophage origin. Here, we review what is known regarding the structure of gap junctions and the mechanisms regulating bone remodeling, and discuss the evidence suggesting that gap junctional intercellular communication contributes to the bone remodeling.
间隙连接是一种特殊的质膜结构，由跨膜通道组成，这些通道直接连接相邻细胞的细胞质，并介导离子和低分子量分子（<1200 Da）的相互交换。结构研究表明，每个间隙连接通道由两个半通道（连接子）的细胞外相互作用形成。每个连接子是蛋白质亚基（连接蛋白）的六聚体组装体，其勾勒出一个水相孔道。连接蛋白是由一个多基因家族编码的同源蛋白，并根据其预测的分子量命名。连接蛋白43广泛分布于不同细胞类型中，是人类骨细胞中表达的主要间隙连接蛋白，尽管也有报道称连接蛋白45和连接蛋白46也有表达。骨重塑需要成骨细胞和破骨细胞之间的协调活动。成骨细胞（骨形成细胞）来源于间充质干细胞，而破骨细胞（骨吸收细胞）是单核细胞/巨噬细胞来源的多核细胞。在此，我们综述了关于间隙连接结构以及调节骨重塑机制的已知内容，并讨论了表明间隙连接细胞间通讯有助于骨重塑的证据。
