Osteocytes are not only mechanoreceptive cells

Osteocytes represent 95% of all bone cells. These cells are old osteoblasts occupying the lacunar space surrounded by the bone matrix. They possess cytoplasmic dendrites that form a canalicular network for communication between osteocytes and the bone surface. They have a mechanosensing role that is dependent upon the frequency, the intensity, and the duration of strain. The mechanical information transmitted into the cytoplasm also triggers a biological cascade, starting with nitric oxide and prostaglandin E 2 and followed by Wnt/ β-catenin signaling. This information is transmitted to the bone surface through the canalicular network, particularly to the lining cells, and is able to trigger bone remodeling by directing the osteoblast activity and the osteoclastic resorption. Furthermore, the osteocyte death seems to play an important role. The outcome of microcracks in the vicinity of osteocytes may interrupt the canalicular network and trigger cell apoptosis in the immediate surrounding environment thus transmitting a message to the bone surface and activate remodeling. This network also plays a recognized endocrine role, particularly concerning phosphate regulation and vitamin D metabolism.