Flow-Induced Migration of Osteoclasts and Regulations of Calcium Signaling Pathways

Abstract

Osteoclasts are large multinucleate cells originating from the fusion of monocytes that are differentiated from hematopoietic stem cells. Although activated osteoclasts preferentially move to the area of microcrack by chemotaxis, whether such mechanical cues as fluid shear stress (FSS) regulate the migration of osteoclasts remains unknown. This study focuses on the effect of FSS on the migration of RAW264.7 monocytes and differentiated osteoclasts, as well as the roles of calcium signaling pathways in cell migration behaviors. We study five calcium signaling pathways, namely, mechanosensitive cation-selective channels (MSCC), phospholipase C, endoplasmic reticulum (ER), adenosine triphosphate, and extracellular calcium. Results show that FSS induces the migration of RAW264.7 cells along flow direction, and the directionality, alignment along the flow direction, and speed of cells are significantly enhanced with the increase in FSS levels. Blocking the pathways of MSCC, ER, or extracellular calcium significantly reduces the migration of RAW264.7 cells along the flow direction. However, the inhibition of calcium signaling pathways does not affect the migration behaviors after inducing RAW264.7 cells for 4 or 8 days with the conditioned medium, Therefore, this study indicates that both undifferentiated monocytes and differentiated osteoclasts tend to migrate along flow direction, furthermore the FSS-induced directional migration of the monocytes is regulated by calcium signaling pathways, but that of differentiated osteoclasts is unaffected.