osteocyten

Osteocytes are mature bone cells derived from osteoblasts that become embedded in the bone matrix during mineralization. They reside in lacunae—small cavities within the mineralized bone—and extend cytoplasmic processes through narrow canaliculi that connect to other osteocytes and to cells on the bone surface.

Together, osteocytes form the osteocyte lacunar-canalicular network, an extensive communication system facilitated by gap junctions, mainly via connexin 43. This network enables nutrient exchange, waste removal, and the rapid transmission of signals throughout the bone.

Function: Osteocytes maintain bone tissue and mineral homeostasis. They regulate remodeling by signaling to osteoblasts and osteoclasts through signaling molecules such as sclerostin (SOST), RANKL, and osteoprotegerin (OPG). They secrete sclerostin to inhibit bone formation when mechanical load is low.

Mechanosensing: Osteocytes act as primary mechanosensors, detecting mechanical strain and fluid flow within the lacunar-canalicular system. Mechanical signals influence remodeling to adapt bone strength to load.

Origin and turnover: Osteocytes originate from osteoblasts that become embedded in the matrix. They are relatively long-lived; some die and are replaced within the bone matrix, while others persist for extended periods, contributing to tissue maintenance.

Clinical relevance: Osteocyte dysfunction is linked to osteoporosis and other metabolic bone diseases. Therapies targeting osteocyte signaling, such as sclerostin inhibitors, aim to enhance bone formation by modulating this network.