Rommel G. Bacabac, Jack J.W.A. Van Loon
Osteocytes are commonly referred to as the professional mechanosensors in bone tissue. Despite recent advances in the study of how bone tissue adapts to mechanical loading, much remains not understood concerning the cellular mechanisms involved. We have shown that bone cell monolayers in vitro release signaling molecules in response to dynamic stress loading in a ratedependent manner. Fluid shear stress induces high release of nitric oxide (NO) at high rates, whereas vibration stress promotes high NO release but low prostaglandin E2 (PGE2) release at high rates, indicating the specificity for signaling molecule of the type of stress. Also, we show evidence that bone cells require a stress threshold in order to respond to loading. These observations collectively provide basis for hypothesizing a model defining tissuemimetic mechanosensitivity as a function of the rate of stress above a threshold. Finally, at the cellular level, we show that shape and stiffness, evidently due to underlying cytoskeletal structure, contribute to mechanosensing. This leads to the notion that the mechanical properties of cells are a prerequisite to their tissue-level emergent mechanosensing behavior. Therefore, a condition of disturbed mechanics due to extreme unloading, as in an environment under microgravity, may lead to impaired mechanosensing. © Springer Science+Business Media, LLC 2010.
Medical Biophysics Group, Department of Physics, University of San Carlos, Nasipit, Talamban, Cebu City 6000, Philippines; Dutch Experiment Support Center, Department of Oral Cell Biology, ACTA-VU University, Amsterdam, Netherlands
