Endocrine Research Unit and Robert and Arlene Kogod Center on Aging, Mayo Clinic, Rochester, MN, 55905.
Division of Orthopedic Research, Mayo Clinic, Rochester, MN, 55905.
J Cell Biochem. 2013 Aug;114(8):1901-1907. doi: 10.1002/jcb.24537.
Osteoclast-mediated bone resorption precedes osteoblast-mediated bone formation through early adulthood, but formation fails to keep pace with resorption during aging. We previously identified several factors produced by osteoclasts that promote bone formation. In this study, we determined if osteoclast-produced factors contribute to the impaired bone formation with aging. We previously found that mice between the ages of 18 and 22 months develop age-related bone loss. Bone marrow-derived pre-osteoclasts were isolated from 6-week, 12-month, and 18- to 24-month-old mice and differentiated into osteoclasts in vitro. Conditioned media were collected and compared for osteoblast mineralization support. Conditioned medium from osteoclasts from all ages was able to support mineralization of bone marrow stromal cells. Concentrating the conditioned medium from 6-week-old and 12-month-old mouse marrow cells-derived osteoclasts enhanced mineralization support whereas concentrated conditioned medium from 18- to 24-month-old mouse marrow-derived osteoclasts repressed mineralization compared to base medium. This observation suggests that an inhibitor of mineralization was secreted by aged murine osteoclasts. Gene and protein analysis revealed that the Wnt antagonist sclerostin was significantly elevated in the conditioned media from 24-month-old mouse cells compared to 6-week-old mouse cells. Antibodies directed to sclerostin neutralized the influences of the aged mouse cell concentrated conditioned media on mineralization. Sclerostin is primarily produced by osteocytes in young animals. This study demonstrates that osteoclasts from aged mice also produce sclerostin in quantities that may contribute to the age-related impairment in bone formation.
破骨细胞介导的骨吸收先于成骨细胞介导的骨形成，贯穿整个成年期，但在衰老过程中，骨形成跟不上骨吸收的速度。我们之前已经鉴定出几种由破骨细胞产生的促进骨形成的因子。在这项研究中，我们确定了破骨细胞产生的因子是否有助于解释衰老导致的骨形成受损。我们之前发现，年龄在 18 至 22 个月的小鼠会出现与年龄相关的骨质流失。从 6 周龄、12 月龄和 18-24 月龄的小鼠中分离骨髓来源的前破骨细胞，并在体外分化为破骨细胞。收集并比较条件培养基对成骨细胞矿化的支持作用。来自所有年龄段的破骨细胞的条件培养基均能支持骨髓基质细胞的矿化。浓缩来自 6 周龄和 12 月龄小鼠骨髓细胞衍生破骨细胞的条件培养基增强了矿化支持作用，而浓缩来自 18-24 月龄小鼠骨髓衍生破骨细胞的条件培养基则抑制了矿化作用，与基础培养基相比。这一观察结果表明，老年鼠破骨细胞分泌了一种矿化抑制剂。基因和蛋白质分析显示，与 6 周龄小鼠细胞相比，来自 24 月龄小鼠细胞的条件培养基中 Wnt 拮抗剂骨硬化蛋白显著升高。针对骨硬化蛋白的抗体中和了来自老年鼠细胞浓缩条件培养基对矿化的影响。骨硬化蛋白主要由幼小动物的成骨细胞产生。本研究表明，老年小鼠的破骨细胞也产生大量的骨硬化蛋白，这可能导致与年龄相关的骨形成受损。
