Mechanical loading effects on bone cells

The skeleton serves as a reservoir for essential minerals, and provides rigid levers for muscles to act against. Although the role of bones in maintaining mineral homeostasis is clearly important, the skeleton's mechanical function certainly has equal importance for the regulation of bone cell biology. During skeletal growth and development, bones must adapt their shape and architecture to make efficient use of material while providing sufficient skeletal strength. This process, termed bone adaptation, requires bone cells to detect mechanical signals in situ and integrate these signals into appropriate changes in the bone architecture. Recent studies have shown that bone adaptation is driven by dynamic, rather than static, loading. Also, it is clear that only a short duration of mechanical loading is necessary to initiate an adaptive response. Finally, bone cells accommodate to a customary mechanical loading environment, making them less responsive to routine loading signals. The mechanism by which cells accommodate is not established, but may involve cytoskeletal reorganization. Cytoskeletal dynamics play a critical role in the transduction of mechanical forces into gene expression. The authors propose that the cytoskeletal architecture in bone cells is determined by the mechanical loading history of the bone tissue. Consequently the mechanosensitivity of bone tissue is dependent upon how much mechanical loading it has received in the past. The ability of an exercise regimen to improve bone density and strength depends upon the mechanosensitivity of the bone tissue, which in turn depends upon past loading history.