Lofthouse R A, Davis J R, Frondoza C G, Jinnah R H, Hungerford D S, Hare J M
Johns Hopkins University, Baltimore, USA.
J Bone Joint Surg Br. 2001 Jan;83(1):124-9. doi: 10.1302/0301-620x.83b1.10604.
Caveolae, specialised regions of the cell membrane which have been detected in a wide range of mammalian cells, have not been described in bone cells. They are plasmalemmal invaginations, 50 to 100 nm in size, characterised by the presence of the structural protein, caveolin, which exists as three subtypes. Caveolin-1 and caveolin-2 are expressed in a wide range of cell types whereas caveolin-3 is thought to be a muscle-specific subtype. There is little information on the precise function of caveolae, but it has been proposed that they play an important role in signal transduction. As the principal bone-producing cell, the osteoblast has been widely studied in an effort to understand the signalling pathways by which it responds to extracellular stimuli. Our aim in this study was to identify caveolae and their structural protein caveolin in normal human osteoblasts, and to determine which subtypes of caveolin were present. Confocal microscopy showed staining which was associated with the plasma membrane. Transmission electron microscopy revealed the presence of membrane invaginations of 50 to 100 nm, consistent with the appearance of caveolae. Finally, we isolated protein from these osteoblasts, and performed Western blotting using anti-caveolin primary antibodies. This revealed the presence of caveolin-1 and -2, while caveolin-3 was absent. The identification of these structures and their associated protein may provide a significant contribution to our further understanding of signal transduction pathways in osteoblasts.
小窝是细胞膜的特殊区域，已在多种哺乳动物细胞中被检测到，但在骨细胞中尚未见报道。它们是质膜内陷，大小为50至100纳米，其特征是存在结构蛋白小窝蛋白，小窝蛋白存在三种亚型。小窝蛋白-1和小窝蛋白-2在多种细胞类型中表达，而小窝蛋白-3被认为是肌肉特异性亚型。关于小窝的确切功能知之甚少，但有人提出它们在信号转导中起重要作用。作为主要的骨生成细胞，成骨细胞已被广泛研究，以了解其对细胞外刺激作出反应的信号通路。本研究的目的是在正常人成骨细胞中鉴定小窝及其结构蛋白小窝蛋白，并确定存在哪些小窝蛋白亚型。共聚焦显微镜显示染色与质膜相关。透射电子显微镜揭示存在50至100纳米的膜内陷，与小窝的外观一致。最后，我们从这些成骨细胞中分离蛋白质，并用抗小窝蛋白一抗进行蛋白质印迹分析。结果显示存在小窝蛋白-1和-2，而小窝蛋白-3不存在。这些结构及其相关蛋白的鉴定可能对我们进一步了解成骨细胞中的信号转导途径有重要贡献。
