The role of osteocytes in bone mechanotransduction

Purpose of review: Significant progress has been made in the field of mechanotransduction in bone cells. The increasing knowledge about the role of the osteocyte as the professional mechanosensor cell of bone, and the lacuno-canalicular porosity as the structure that mediates mechanosensing, might result in a new paradigm for understanding the bone formation response to mechanical loading, and the bone resorption response to disuse. Strain-derived flow of interstitial fluid through the lacuno-canalicular porosity seems to mechanically activate the osteocytes, as well as ensures transport of cell signaling molecules, nutrients, and waste products. This concept allows explanation of local bone gain and loss, as well as remodeling in response to fatigue damage, as processes supervised by mechanosensitive osteocytes. Recent findings: The osteogenic activity of bone cells in vitro have been quantitatively correlated with varying stress stimulations highlighting the importance of the rate of loading. Theoretically, a possible mechanism for the stress response by osteocytes is due to strain-amplification at the pericellular matrix. Hence, single cell studies on molecular responses of osteocytes are on their way. These findings contribute insight on local architectural alignment in bone during remodeling. Alignment seems to occur as a result of the osteocyte's sensing different canalicular flow patterns around cutting cone and reversal zone during loading, thus determining the bone's structure. Summary: Uncovering the cellular and mechanical basis of the osteocyte's response to loading represents a significant challenge to our understanding of cellular mechanotransduction and bone remodeling.