PURPOSE OF REVIEW: Bone cells such as osteoclasts, osteoblasts, and osteocytes 'talk' to each other throughout adult life to maintain bone integrity. This review highlights frontier areas of research on intercellular communication among bone cells. RECENT FINDINGS: Bone cells communicate to regulate the balance between bone resorption and bone formation. Recent findings have suggested that bone remodeling compartment is critical for osteoclast-osteoblast communication during bone remodeling. New molecules and mechanisms for bone cell communication, including 'coupling' of bone formation to resorption, have been revealed. Osteoclastic regulation of pH within the bone remodeling compartment is a mechanism that has been posited to rapidly activate osteoblastic bone formation, whereas osteocytes in the bone matrix regulate osteoclasts and osteoblasts on the bone surface through the lacuno-canaliculi network. SUMMARY: Differentiation, activation, and apoptosis of bone cells are often dependent on the status of other types of bone cells. Bone cells in different lineages achieve intercellular communication not only by ligand-receptor interactions but also by molecules and ions traveling in the extracellular space or across gap junctions, processes that depend profoundly on the four-dimensional (space and time) architecture of bone tissue.
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