Osteocytes, osteoblasts (bone-forming cells), and osteoclasts (bone-resorbing cells) are the primary types of cells that regulate bone metabolism in mammals. Sclerostin produced in bone cells activates osteoclasts, inhibiting bone formation; excess production of sclerostin, therefore, leads to the loss of bone mass. Fish scales have been reported to have morphological and functional similarities to mammalian bones, making them a useful experimental system for analyzing vertebrate bone metabolism in vitro. However, whether fish scales contain cells producing sclerostin and/or osteocytes has not been determined. The current study demonstrated, for the first time, that sclerostin-containing cells exist in goldfish scales. Analysis of the distribution and shape of sclerostin-expressing cells provided evidence that osteoblasts produce sclerostin in goldfish scales. Furthermore, our results found that osteocyte-like cells exist in goldfish scales, which also produce sclerostin. Finally, we demonstrated that microgravity in outer space increased the level of sclerostin in the scales of goldfish, a finding suggesting that the induction of sclerostin is the mechanism underlying the activation of osteoclasts under microgravity.

骨细胞、成骨细胞（骨形成细胞）和破骨细胞（骨吸收细胞）是调节哺乳动物骨代谢的主要细胞类型。骨细胞中产生的硬化蛋白激活破骨细胞，抑制骨形成；因此，过量产生的硬化蛋白会导致骨量减少。据报道，鱼鳞在形态和功能上与哺乳动物骨骼相似，使其成为体外分析脊椎动物骨骼代谢的有用实验系统. 然而，鱼鳞是否含有产生硬化蛋白和/或骨细胞的细胞尚未确定。目前的研究首次证明，金鱼鳞片中存在含有硬化蛋白的细胞。对表达硬化蛋白的细胞的分布和形状的分析提供了成骨细胞在金鱼鳞片中产生硬化蛋白的证据。此外，我们的结果发现金鱼鳞片中存在骨细胞样细胞，其也产生硬化蛋白。最后，我们证明了外层空间的微重力增加了金鱼鳞片中硬化蛋白的水平，这一发现表明硬化蛋白的诱导是微重力下破骨细胞活化的机制。