Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.
Department of Maxillofacial Orthognathics, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
J Cell Physiol. 2018 Jan;233(1):259-268. doi: 10.1002/jcp.25872. Epub 2017 May 3.
Osteocytes are the most abundant cells in bone and regulate bone metabolism in coordination with osteoblasts and osteoclasts. However, the molecules that control osteocytes are still incompletely understood. Profilin1 is an actin-binding protein that is involved in actin polymerization. Osteocytes possess characteristic dendritic process formed based on actin cytoskeleton. Here, we examined the expression of profilin1 and its function in osteocytes. Profilin1 mRNA was expressed in osteocytic MLO-Y4 cells and its levels were gradually increased along with the time in culture. With regard to functional aspect, knockdown of profilin1 by siRNA enhanced BMP-induced increase in alkaline phosphatase expression levels in MLO-Y4 cells. Profilin1 knockdown suppressed the levels of dendritic processes and migration of MLO-Y4 cells. Since aging causes an increase in ROS in the body, we further examined the effects of hydrogen peroxide on the expression of profilin1. Hydrogen peroxide treatment increased the levels of profilin1 mRNA in MLO-Y4 cells in contrast to the decline in alkaline phosphatase. Profilin1 was expressed not only in MLO-Y4cells but also in the primary cultures of osteocytes. Importantly, profilin1 mRNA levels in primary cultures of osteocytes were higher than those in primary cultures of osteoblasts. To examine in vivo role of profilin1 in osteocytes, profilin1 was conditionally knocked out by using DMP1-cre and profilin1 floxed mice. This conditional deletion of profilin1 specifically in osteocytes resulted in reduction in the levels of bone volume and bone mineral density. These data indicate that profilin1 is expressed in osteocytes and regulates cell shape, migration and bone mass.
骨细胞是骨中最丰富的细胞，与成骨细胞和破骨细胞协同调节骨代谢。然而，控制骨细胞的分子仍不完全清楚。丝状肌动蛋白结合蛋白 Profilin1 参与肌动蛋白聚合。骨细胞具有基于肌动蛋白细胞骨架形成的特征性树突状突起。在这里，我们研究了 Profilin1 的表达及其在骨细胞中的功能。Profilin1mRNA 在成骨细胞样 MLO-Y4 细胞中表达，其水平随着培养时间的延长而逐渐增加。关于功能方面，siRNA 敲低 Profilin1 增强了 BMP 诱导的 MLO-Y4 细胞中碱性磷酸酶表达水平的增加。Profilin1 敲低抑制了 MLO-Y4 细胞树突状突起和迁移的水平。由于衰老会导致体内 ROS 增加，我们进一步研究了过氧化氢对 Profilin1 表达的影响。与碱性磷酸酶水平下降相反，过氧化氢处理增加了 MLO-Y4 细胞中 Profilin1mRNA 的水平。Profilin1 不仅在 MLO-Y4 细胞中表达，而且在成骨细胞的原代培养物中表达。重要的是，成骨细胞原代培养物中的 Profilin1mRNA 水平高于成骨细胞原代培养物。为了研究 Profilin1 在骨细胞中的体内作用，我们使用 DMP1-cre 和 Profilin1 floxed 小鼠对 Profilin1 进行条件性敲除。这种在骨细胞中特异性敲除 Profilin1 导致骨量和骨矿物质密度的降低。这些数据表明 Profilin1 在骨细胞中表达，并调节细胞形状、迁移和骨量。
