[Apoptosis--basic regulatory mechanism of bone remodeling].

Bone remodeling and regeneration take place permanently and are the result of a perfect balance between osteoclastic bone resorption and osteoblastic bone synthesis performed in the bone multicellular unit. Osteoblasts and osteoclasts differentiate from precursors under the influence of cytokines, growth factors mand cellular interactions controlled by adhesion molecules. The same growth factors and cytokines that promote bone cell differentiation have an important role in the prevention of cell death that is usually produced by apoptosis. The molecular mechanism of cytokines' and growth factors' actions is the activation of the pathway glicoprotein 130/Janus kinases/signal transductors and activators of transcription. The final step is the inhibition of cycline-dependent kinases, resulting in the inhibition of cell cycle and transition from G1 phase to S phase. Osteoblastogenesis and osteoclastogenesis are strongly bound together. Osteocytes are the most numerous bone cells, they have a long life, but ultimately die by apoptosis.