Osteocytes in Normal Physiology and Osteoporosis

Osteoporosis is characterized by the reduced mass as well as quality of bone, and increased risk of fragility fracture. Skeletal homeostasis is maintained through the balanced activities of osteoclasts and osteoblasts, and osteoporosis is considered to be a metabolic disorder caused by an imbalance between bone resorption and formation. Whereas osteoclasts and osteoblasts have been the primary targets for elucidating the cell-based mechanisms underlying the pathophysiology of osteoporosis, much less attention has been paid to the role of osteocytes. This review focuses on the physiologic function of osteocytes in the regulation of bone and mineral metabolism, summarizing the findings from human disease and mouse genetics, and then extending the discussion to the pathogenetic roles of osteocytes in skeletal aging.