[Space flight/bedrest immobilization and bone. Osteocyte as a sensor of mechanical stress and Wnt signal]

Osteocytes sense mechanical stress. Many long cell processes of osteocytes connect with osteoblasts and osteoclasts as well as other osteocytes. Tethering elements on the cell processes amplify mechanical strain. Primary cilia of osteocytes and integrin of extracellular matrix act as mechnosensors. Osteocytes express RANKL. The disruption of osteocyte-specific RANKL leads to osteopetrosis. Mechanical stress reduced sclerostin expression. Sclerostin suppresses osteoblastic function by inhibiting Wnt/β-catenin pathway. The disruption of SOST gene encoding sclerostin causes resistance to the reduction of bone formation after skeletal unloading. Osteocytes play an important role in regulating bone remodeling as well as sensing mechanical stress.